DBMS ############################## 1. What is database? A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose. 2. What is DBMS? It is a collection of programs that enables user to create and maintain a database. In other words it is general- purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications. 3. What is a Database system? The database and DBMS software together is called as Database system. 4. Advantages of DBMS? Ø Redundancy is controlled. Ø Unauthorised access is restricted. Ø Providing multiple user interfaces. Ø Enforcing integrity constraints. Ø Providing backup and recovery. 5. Disadvantage in File Processing System? Ø Data redundancy & inconsistency. Ø Difficult in accessing data. Ø Data isolation. Ø Data integrity. Ø Concurrent access is not possible. Ø Security Problems. 6. Describe the three levels of data abstraction? The are three levels of abstraction: Ø Physical level: The lowest level of abstraction describes how data are stored. Ø Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data. Ø View level: The highest level of abstraction describes only part of entire database. 7. Define the "integrity rules" There are two Integrity rules. Ø Entity Integrity: States that “Primary key cannot have NULL value” Ø Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation. 8. What is extension and intension? Extension - It is the number of tuples present in a table at any instance. This is time dependent. Intension - It is a constant value that gives the name, structure of table and the constraints laid on it. 9. What is System R? What are its two major subsystems? System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system. Its two subsystems are Ø Research Storage Ø System Relational Data System. 10. How is the data structure of System R different from the relational structure? Unlike Relational systems in System R Ø Domains are not supported Ø Enforcement of candidate key uniqueness is optional Ø Enforcement of entity integrity is optional
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DBMS##############################1. What is database?
A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.
2. What is DBMS?It is a collection of programs that enables user to create and maintain a database. In other words it is general-purpose software that provides the users with the processes of defining, constructing and manipulating the database for various applications.
3. What is a Database system?The database and DBMS software together is called as Database system.
4. Advantages of DBMS?Ø Redundancy is controlled.Ø Unauthorised access is restricted.Ø Providing multiple user interfaces.Ø Enforcing integrity constraints.Ø Providing backup and recovery.
5. Disadvantage in File Processing System?Ø Data redundancy & inconsistency.Ø Difficult in accessing data.Ø Data isolation.Ø Data integrity.Ø Concurrent access is not possible.Ø Security Problems.
6. Describe the three levels of data abstraction?The are three levels of abstraction:Ø Physical level: The lowest level of abstraction describes how data are stored.Ø Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.Ø View level: The highest level of abstraction describes only part of entire database. 7. Define the "integrity rules"There are two Integrity rules.Ø Entity Integrity: States that “Primary key cannot have NULL value”Ø Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.
8. What is extension and intension?Extension -It is the number of tuples present in a table at any instance. This is time dependent.Intension -
It is a constant value that gives the name, structure of table and the constraints laid on it.
9. What is System R? What are its two major subsystems?System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.Its two subsystems areØ Research StorageØ System Relational Data System.
10. How is the data structure of System R different from the relational structure?Unlike Relational systems in System RØ Domains are not supportedØ Enforcement of candidate key uniqueness is optionalØ Enforcement of entity integrity is optionalØ Referential integrity is not enforced
11. What is Data Independence?Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.Two types of Data Independence:Ø Physical Data Independence: Modification in physical level should not affect the logical level.Ø Logical Data Independence: Modification in logical level should affect the view level.NOTE: Logical Data Independence is more difficult to achieve 12. What is a view? How it is related to data independence?A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary.Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.
13. What is Data Model?A collection of conceptual tools for describing data, data relationships data semantics and constraints.
14. What is E-R model?This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
15. What is Object Oriented model?
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
16. What is an Entity?It is a 'thing' in the real world with an independent existence.
17. What is an Entity type?It is a collection (set) of entities that have same attributes.
18. What is an Entity set?It is a collection of all entities of particular entity type in the database.
19. What is an Extension of entity type?The collections of entities of a particular entity type are grouped together into an entity set.
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20. What is Weak Entity set?An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.
21. What is an attribute?It is a particular property, which describes the entity.
22. What is a Relation Schema and a Relation?A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains. A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).
23. What is degree of a Relation?It is the number of attribute of its relation schema.
24. What is Relationship?It is an association among two or more entities.
25. What is Relationship set?The collection (or set) of similar relationships.
26. What is Relationship type?Relationship type defines a set of associations or a relationship set among a given set of entity types.
27. What is degree of Relationship type?It is the number of entity type participating.
25. What is DDL (Data Definition Language)?A data base schema is specifies by a set of definitions expressed by a special language called DDL.
26. What is VDL (View Definition Language)?It specifies user views and their mappings to the conceptual schema.
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27. What is SDL (Storage Definition Language)?This language is to specify the internal schema. This language may specify the mapping between two schemas.
28. What is Data Storage - Definition Language?The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.
29. What is DML (Data Manipulation Language)?This language that enable user to access or manipulate data as organised by appropriate data model.Ø Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data.Ø Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data.
31. What is DML Compiler?It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
32. What is Query evaluation engine?It executes low-level instruction generated by compiler.
33. What is DDL Interpreter?It interprets DDL statements and record them in tables containing metadata.
34. What is Record-at-a-time?The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.
35. What is Set-at-a-time or Set-oriented?The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.
36. What is Relational Algebra?It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.
37. What is Relational Calculus?It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.
38. How does Tuple-oriented relational calculus differ from domain-oriented relational calculusThe tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUELThe domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.
39. What is normalization?It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the propertiesØ Minimizing redundancyØ Minimizing insertion, deletion and update anomalies.
40. What is Functional Dependency?A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.
41. When is a functional dependency F said to be minimal?Ø Every dependency in F has a single attribute for its right hand side.Ø We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.Ø We cannot remove any dependency from F and still have set of dependency that is equivalent to F.
42. What is Multivalued dependency?Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following propertiesØ t3[x] = t4[X] = t1[X] = t2[X]Ø t3[Y] = t1[Y] and t4[Y] = t2[Y]Ø t3[Z] = t2[Z] and t4[Z] = t1[Z]where [Z = (R-(X U Y)) ]43. What is Lossless join property?It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
44. What is 1 NF (Normal Form)?The domain of attribute must include only atomic (simple, indivisible) values.
45. What is Fully Functional dependency?It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
46. What is 2NF?A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
47. What is 3NF?A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is trueØ X is a Super-key of R.Ø A is a prime attribute of R.In other words, if every non prime attribute is non-transitively dependent on primary key.
48. What is BCNF (Boyce-Codd Normal Form)?A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.
49. What is 4NF?A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is trueØ X is subset or equal to (or) XY = R.Ø X is a super key.
50. What is 5NF?A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is trueØ Ri = R for some i.Ø The join dependency is implied by the set of FD, over R in which the left side is key of R. 51. What is Domain-Key Normal Form?A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.
52. What are partial, alternate,, artificial, compound and natural key?Partial Key:It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.Alternate Key:All Candidate Keys excluding the Primary Key are known as Alternate Keys.Artificial Key:If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.Compound Key:If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.Natural Key:
When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.
53. What is indexing and what are the different kinds of indexing?Indexing is a technique for determining how quickly specific data can be found.Types:Ø Binary search style indexingØ B-Tree indexingØ Inverted list indexingØ Memory resident tableØ Table indexing
54. What is system catalog or catalog relation? How is better known as?A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.55. What is meant by query optimization?The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.
56. What is join dependency and inclusion dependency?Join Dependency:A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.Inclusion Dependency:An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.
57. What is durability in DBMS?Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.
58. What do you mean by atomicity and aggregation?Atomicity:Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.Aggregation:A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.
59. What is a Phantom Deadlock?
In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.
60. What is a checkpoint and When does it occur?A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.61. What are the different phases of transaction?Different phases areØ Analysis phaseØ Redo PhaseØ Undo phase
62. What do you mean by flat file database?It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.
63. What is "transparent DBMS"?It is one, which keeps its Physical Structure hidden from user.
64. Brief theory of Network, Hierarchical schemas and their propertiesNetwork schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.
65. What is a query?A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.
66. What do you mean by Correlated subquery?Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery.A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)
67. What are the primitive operations common to all record management systems?Addition, deletion and modification.
68. Name the buffer in which all the commands that are typed in are stored‘Edit’ Buffer
69. What are the unary operations in Relational Algebra?PROJECTION and SELECTION.
70. Are the resulting relations of PRODUCT and JOIN operation the same?No.PRODUCT: Concatenation of every row in one relation with every row in another.JOIN: Concatenation of rows from one relation and related rows from another.
71. What is RDBMS KERNEL?Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the databaseYou might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures.72. Name the sub-systems of a RDBMSI/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management
73. Which part of the RDBMS takes care of the data dictionary? HowData dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.
74. What is the job of the information stored in data-dictionary?The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.
75. Not only RDBMS takes care of locating data it alsodetermines an optimal access path to store or retrieve the data
76. How do you communicate with an RDBMS?You communicate with an RDBMS using Structured Query Language (SQL)
77. Define SQL and state the differences between SQL and other conventional programming Languages
SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.
78. Name the three major set of files on disk that compose a database in OracleThere are three major sets of files on disk that compose a database. All the files are binary. These areØ Database filesØ Control filesØ Redo logsThe most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself.All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.
79. What is an Oracle Instance?The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselvesOracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them.The combination of the SGA and the Oracle background processes is known as an Oracle instance
80. What are the four Oracle system processes that must always be up and running for the database to be useableThe four Oracle system processes that must always be up and running for the database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process Monitor).81. What are database files, control files and log files. How many of these files should a database have at least? Why?Database FilesThe database files hold the actual data and are typically the largest in size. Depending on their sizes, the tables (and other objects) for all the user accounts can go in one database file—but that's not an ideal situation because it does not make the database structure very flexible for controlling access to storage for different users, putting the database on different disk drives, or backing up and restoring just part of the database.You must have at least one database file but usually, more than one files are used. In terms of accessing and using the data in the tables and other objects, the number (or location) of the files is immaterial.
The database files are fixed in size and never grow bigger than the size at which they were createdControl FilesThe control files and redo logs support the rest of the architecture. Any database must have at least one control file, although you typically have more than one to guard against loss. The control file records the name of the database, the date and time it was created, the location of the database and redo logs, and the synchronization information to ensure that all three sets of files are always in step. Every time you add a new database or redo log file to the database, the information is recorded in the control files.Redo LogsAny database must have at least two redo logs. These are the journals for the database; the redo logs record all changes to the user objects or system objects. If any type of failure occurs, the changes recorded in the redo logs can be used to bring the database to a consistent state without losing any committed transactions. In the case of non-data loss failure, Oracle can apply the information in the redo logs automatically without intervention from the DBA.The redo log files are fixed in size and never grow dynamically from the size at which they were created.
82. What is ROWID?The ROWID is a unique database-wide physical address for every row on every table. Once assigned (when the row is first inserted into the database), it never changes until the row is deleted or the table is dropped.The ROWID consists of the following three components, the combination of which uniquely identifies the physical storage location of the row.Ø Oracle database file number, which contains the block with the rowsØ Oracle block address, which contains the rowØ The row within the block (because each block can hold many rows)The ROWID is used internally in indexes as a quick means of retrieving rows with a particular key value. Application developers also use it in SQL statements as a quick way to access a row once they know the ROWID
83. What is Oracle Block? Can two Oracle Blocks have the same address?Oracle "formats" the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.
84. What is database Trigger?A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire statement or once for every row that is inserted, updated, or deleted. For any one table, there are twelve events for which you can define database triggers. A database trigger can call database procedures that are also written in PL/SQL.
85. Name two utilities that Oracle provides, which are use for backup and recovery.Along with the RDBMS software, Oracle provides two utilities that you can use to back up and restore the database. These utilities are Export and Import.The Export utility dumps the definitions and data for the specified part of the database to an operating system binary file. The Import utility reads the file produced by an export, recreates the definitions of objects, and inserts the dataIf Export and Import are used as a means of backing up and recovering the database, all the changes made to the database cannot be recovered since the export was performed. The best you can do is recover the database to the time when the export was last performed.
86. What are stored-procedures? And what are the advantages of using them.Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns the result to the client. Stored procedures are used to reduce network traffic.
87. How are exceptions handled in PL/SQL? Give some of the internal exceptions' namePL/SQL exception handling is a mechanism for dealing with run-time errors encountered during procedure execution. Use of this mechanism enables execution to continue if the error is not severe enough to cause procedure termination.The exception handler must be defined within a subprogram specification. Errors cause the program to raise an exception with a transfer of control to the exception-handler block. After the exception handler executes, control returns to the block in which the handler was defined. If there are no more executable statements in the block, control returns to the caller.User-Defined ExceptionsPL/SQL enables the user to define exception handlers in the declarations area of subprogram specifications. User accomplishes this by naming an exception as in the following example:ot_failure EXCEPTION;
In this case, the exception name is ot_failure. Code associated with this handler is written in the EXCEPTION specification area as follows:EXCEPTIONwhen OT_FAILURE thenout_status_code := g_out_status_code;out_msg := g_out_msg;The following is an example of a subprogram exception:EXCEPTIONwhen NO_DATA_FOUND theng_out_status_code := 'FAIL';RAISE ot_failure;Within this exception is the RAISE statement that transfers control back to the ot_failure exception handler. This technique of raising the exception is used to invoke all user-defined exceptions.System-Defined ExceptionsExceptions internal to PL/SQL are raised automatically upon error. NO_DATA_FOUND is a system-defined exception. Table below gives a complete list of internal exceptions.
In addition to this list of exceptions, there is a catch-all exception named OTHERS that traps all errors for which specific error handling has not been established.
88. Does PL/SQL support "overloading"? ExplainThe concept of overloading in PL/SQL relates to the idea that you can define procedures and functions with the same name. PL/SQL does not look only at the referenced name, however, to resolve a procedure or function call. The count and data types of formal parameters are also considered.PL/SQL also attempts to resolve any procedure or function calls in locally defined packages before looking at globally defined packages or internal functions. To further ensure calling the proper procedure, you can use the dot notation. Prefacing a procedure or function name with the package name fully qualifies any procedure or function reference.
89. Tables derived from the ERD
a) Are totally unnormalisedb) Are always in 1NFc) Can be further denormalisedd) May have multi-valued attributes
(b) Are always in 1NF
90. Spurious tuples may occur due toi. Bad normalizationii. Theta joinsiii. Updating tables from joina) i & ii b) ii & iiic) i & iii d) ii & iii
(a) i & iii because theta joins are joins made on keys that are not primary keys.
91. A B C is a set of attributes. The functional dependency is as followsAB -> BAC -> CC -> Ba) is in 1NFb) is in 2NFc) is in 3NFd) is in BCNF
(a) is in 1NF since (AC)+ = { A, B, C} hence AC is the primary key. Since C B is a FD given, where neither C is a Key nor B is a prime attribute, this it is not in 3NF. Further B is not functionally dependent on key AC thus it is not in 2NF. Thus the given FDs is in 1NF.
92. In mapping of ERD to DFDa) entities in ERD should correspond to an existing entity/store in DFDb) entity in DFD is converted to attributes of an entity in ERDc) relations in ERD has 1 to 1 correspondence to processes in DFDd) relationships in ERD has 1 to 1 correspondence to flows in DFD
(a) entities in ERD should correspond to an existing entity/store in DFD
93. A dominant entity is the entitya) on the N side in a 1 : N relationshipb) on the 1 side in a 1 : N relationshipc) on either side in a 1 : 1 relationshipd) nothing to do with 1 : 1 or 1 : N relationship
(b) on the 1 side in a 1 : N relationship94. Select 'NORTH', CUSTOMER From CUST_DTLS Where REGION = 'N' Order ByCUSTOMER Union Select 'EAST', CUSTOMER From CUST_DTLS Where REGION = 'E' Order By CUSTOMERThe above is
a) Not an errorb) Error - the string in single quotes 'NORTH' and 'SOUTH'c) Error - the string should be in double quotesd) Error - ORDER BY clause
(d) Error - the ORDER BY clause. Since ORDER BY clause cannot be used in UNIONS
95. What is Storage Manager?It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.
96. What is Buffer Manager?It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.
97. What is Transaction Manager?It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.
98. What is File Manager?It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.
99. What is Authorization and Integrity manager?It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.
100. What are stand-alone procedures?Procedures that are not part of a package are known as stand-alone because they independently defined. A good example of a stand-alone procedure is one written in a SQL*Forms application. These types of procedures are not available for reference from other Oracle tools. Another limitation of stand-alone procedures is that they are compiled at run time, which slows execution.
101. What are cursors give different types of cursors.PL/SQL uses cursors for all database information accesses statements. The language supports the use two types of cursorsØ ImplicitØ Explicit
102. What is cold backup and hot backup (in case of Oracle)?Ø Cold Backup:It is copying the three sets of files (database files, redo logs, and control file) when the instance is shut down. This is a straight file copy, usually from the disk directly to tape. You must shut down the instance to guarantee a consistent copy.
If a cold backup is performed, the only option available in the event of data file loss is restoring all the files from the latest backup. All work performed on the database since the last backup is lost.Ø Hot Backup:Some sites (such as worldwide airline reservations systems) cannot shut down the database while making a backup copy of the files. The cold backup is not an available option.So different means of backing up database must be used — the hot backup. Issue a SQL command to indicate to Oracle, on a tablespace-by-tablespace basis, that the files of the tablespace are to backed up. The users can continue to make full use of the files, including making changes to the data. Once the user has indicated that he/she wants to back up the tablespace files, he/she can use the operating system to copy those files to the desired backup destination.The database must be running in ARCHIVELOG mode for the hot backup option.If a data loss failure does occur, the lost database files can be restored using the hot backup and the online and offline redo logs created since the backup was done. The database is restored to the most consistent state without any loss of committed transactions.
103. What are Armstrong rules? How do we say that they are complete and/or soundThe well-known inference rules for FDsØ Reflexive rule :If Y is subset or equal to X then X Y.Ø Augmentation rule:If X Y then XZ YZ.Ø Transitive rule:If {X Y, Y Z} then X Z.Ø Decomposition rule :
If X YZ then X Y.Ø Union or Additive rule:If {X Y, X Z} then X YZ.Ø Pseudo Transitive rule :If {X Y, WY Z} then WX Z.Of these the first three are known as Amstrong Rules. They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules.
104. How can you find the minimal key of relational schema?Minimal key is one which can identify each tuple of the given relation schema uniquely. For finding the minimal key it is required to find the closure that is the set of all attributes that are dependent on any given set of attributes under the given set of functional dependency.Algo. I Determining X+, closure for X, given set of FDs F1. Set X+ = X2. Set Old X+ = X+3. For each FD Y Z in F and if Y belongs to X+ then add Z to X+4. Repeat steps 2 and 3 until Old X+ = X+
Algo.II Determining minimal K for relation schema R, given set of FDs F1. Set K to R that is make K a set of all attributes in R2. For each attribute A in Ka. Compute (K – A)+ with respect to Fb. If (K – A)+ = R then set K = (K – A)+
105. What do you understand by dependency preservation?Given a relation R and a set of FDs F, dependency preservation states that the closure of the union of the projection of F on each decomposed relation Ri is equal to the closure of F. i.e.,((PR1(F)) U … U (PRn(F)))+ = F+if decomposition is not dependency preserving, then some dependency is lost in the decomposition.
106. What is meant by Proactive, Retroactive and Simultaneous Update.Proactive Update:The updates that are applied to database before it becomes effective in real world .Retroactive Update:The updates that are applied to database after it becomes effective in real world .Simulatneous Update:The updates that are applied to database at the same time when it becomes effective in real world .
107. What are the different types of JOIN operations?Equi Join: This is the most common type of join which involves only equality comparisions. The disadvantage in this type of join is that there
FAQ In SQL
1. Which is the subset of SQL commands used to manipulate Oracle Database structures, including tables?Data Definition Language (DDL)
2. What operator performs pattern matching?LIKE operator
3. What operator tests column for the absence of data?IS NULL operator
4. Which command executes the contents of a specified file?START <filename> or @<filename>
5. What is the parameter substitution symbol used with INSERT INTO command?&
6. Which command displays the SQL command in the SQL buffer, and then executes it?RUN
7. What are the wildcards used for pattern matching?_ for single character substitution and % for multi-character substitution
8. State true or false. EXISTS, SOME, ANY are operators in SQL.True
9. State true or false. !=, <>, ^= all denote the same operation.True
10. What are the privileges that can be granted on a table by a user to others?Insert, update, delete, select, references, index, execute, alter, all
11. What command is used to get back the privileges offered by the GRANT command?REVOKE
12. Which system tables contain information on privileges granted and privileges obtained?USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD
13. Which system table contains information on constraints on all the tables created?USER_CONSTRAINTS
14. TRUNCATE TABLE EMP;DELETE FROM EMP;Will the outputs of the above two commands differ?Both will result in deleting all the rows in the table EMP.
15. What is the difference between TRUNCATE and DELETE commands?TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.
16. What command is used to create a table by copying the structure of another table?Answer :CREATE TABLE .. AS SELECT commandExplanation :To copy only the structure, the WHERE clause of the SELECT command should contain a FALSE statement as in the following.CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1=2;If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table.17. What will be the output of the following query?SELECT REPLACE(TRANSLATE(LTRIM(RTRIM('!! ATHEN !!','!'), '!'), 'AN', '**'),'*','TROUBLE') FROM DUAL;
TROUBLETHETROUBLE
18. What will be the output of the following query?SELECT DECODE(TRANSLATE('A','1234567890','1111111111'), '1','YES', 'NO' );Answer :NOExplanation :The query checks whether a given string is a numerical digit.
19. What does the following query do?SELECT SAL + NVL(COMM,0) FROM EMP;This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.
20. Which date function is used to find the difference between two dates?MONTHS_BETWEEN
21. Why does the following command give a compilation error?DROP TABLE &TABLE_NAME;Variable names should start with an alphabet. Here the table name starts with an '&' symbol.
22. What is the advantage of specifying WITH GRANT OPTION in the GRANT command?The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user.
23. What is the use of the DROP option in the ALTER TABLE command?It is used to drop constraints specified on the table.
24. What is the value of ‘comm’ and ‘sal’ after executing the following query if the initial value of ‘sal’ is 10000?UPDATE EMP SET SAL = SAL + 1000, COMM = SAL*0.1;sal = 11000, comm = 1000
25. What is the use of DESC in SQL?Answer :DESC has two purposes. It is used to describe a schema as well as to retrieve rows from table in descending order.Explanation :The query SELECT * FROM EMP ORDER BY ENAME DESC will display the output sorted on ENAME in descending order.
26. What is the use of CASCADE CONSTRAINTS?When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.
27. Which function is used to find the largest integer less than or equal to a specific value?
FLOOR
28. What is the output of the following query?SELECT TRUNC(1234.5678,-2) FROM DUAL;1200
PNAME (VARCHAR), TITLE (VARCHAR), DEVIN (VARCHAR), SCOST (NUMBER), DCOST (NUMBER), SOLD (NUMBER)
Table 3 : PROGRAMMER
PNAME (VARCHAR), DOB (DATE), DOJ (DATE), SEX (CHAR), PROF1 (VARCHAR), PROF2 (VARCHAR), SAL (NUMBER)LEGEND :
PNAME – Programmer Name, SPLACE – Study Place, CCOST – Course Cost, DEVIN – Developed in, SCOST – Software Cost, DCOST – Development Cost, PROF1 – Proficiency 1
QUERIES :
1. Find out the selling cost average for packages developed in Oracle.2. Display the names, ages and experience of all programmers.3. Display the names of those who have done the PGDCA course.4. What is the highest number of copies sold by a package?5. Display the names and date of birth of all programmers born in April.6. Display the lowest course fee.7. How many programmers have done the DCA course.8. How much revenue has been earned through the sale of packages developed in C.9. Display the details of software developed by Rakesh.10. How many programmers studied at Pentafour.11. Display the details of packages whose sales crossed the 5000 mark.
12. Find out the number of copies which should be sold in order to recover the development cost of each package.13. Display the details of packages for which the development cost has been recovered.14. What is the price of costliest software developed in VB?15. How many packages were developed in Oracle ?16. How many programmers studied at PRAGATHI?17. How many programmers paid 10000 to 15000 for the course?18. What is the average course fee?19. Display the details of programmers knowing C.20. How many programmers know either C or Pascal?21. How many programmers don’t know C and C++?22. How old is the oldest male programmer?23. What is the average age of female programmers?24. Calculate the experience in years for each programmer and display along with their names in descending order.25. Who are the programmers who celebrate their birthdays during the current month? 26. How many female programmers are there?27. What are the languages known by the male programmers?28. What is the average salary?29. How many people draw 5000 to 7500?30. Display the details of those who don’t know C, C++ or Pascal.31. Display the costliest package developed by each programmer.32. Produce the following output for all the male programmersProgrammerMr. Arvind – has 15 years of experience
KEYS:
1. SELECT AVG(SCOST) FROM SOFTWARE WHERE DEVIN = 'ORACLE';
2. SELECT PNAME,TRUNC(MONTHS_BETWEEN(SYSDATE,DOB)/12) "AGE", TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) "EXPERIENCE" FROM PROGRAMMER;
3. SELECT PNAME FROM STUDIES WHERE COURSE = 'PGDCA';
4. SELECT MAX(SOLD) FROM SOFTWARE;
5. SELECT PNAME, DOB FROM PROGRAMMER WHERE DOB LIKE '%APR%';
6. SELECT MIN(CCOST) FROM STUDIES;
7. SELECT COUNT(*) FROM STUDIES WHERE COURSE = 'DCA';
8. SELECT SUM(SCOST*SOLD-DCOST) FROM SOFTWARE GROUP BY DEVIN HAVING DEVIN = 'C';
9. SELECT * FROM SOFTWARE WHERE PNAME = 'RAKESH';
10. SELECT * FROM STUDIES WHERE SPLACE = 'PENTAFOUR';
11. SELECT * FROM SOFTWARE WHERE SCOST*SOLD-DCOST > 5000;
12. SELECT CEIL(DCOST/SCOST) FROM SOFTWARE;
13. SELECT * FROM SOFTWARE WHERE SCOST*SOLD >= DCOST;
14. SELECT MAX(SCOST) FROM SOFTWARE GROUP BY DEVIN HAVING DEVIN = 'VB';
15. SELECT COUNT(*) FROM SOFTWARE WHERE DEVIN = 'ORACLE';
16. SELECT COUNT(*) FROM STUDIES WHERE SPLACE = 'PRAGATHI';
17. SELECT COUNT(*) FROM STUDIES WHERE CCOST BETWEEN 10000 AND 15000;
18. SELECT AVG(CCOST) FROM STUDIES;
19. SELECT * FROM PROGRAMMER WHERE PROF1 = 'C' OR PROF2 = 'C';
20. SELECT * FROM PROGRAMMER WHERE PROF1 IN ('C','PASCAL') OR PROF2 IN ('C','PASCAL');
21. SELECT * FROM PROGRAMMER WHERE PROF1 NOT IN ('C','C++') AND PROF2 NOT IN ('C','C++');
22. SELECT TRUNC(MAX(MONTHS_BETWEEN(SYSDATE,DOB)/12)) FROM PROGRAMMER WHERE SEX = 'M';
23. SELECT TRUNC(AVG(MONTHS_BETWEEN(SYSDATE,DOB)/12)) FROM PROGRAMMER WHERE SEX = 'F';
24. SELECT PNAME, TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) FROM PROGRAMMER ORDER BY PNAME DESC;
25. SELECT PNAME FROM PROGRAMMER WHERE TO_CHAR(DOB,'MON') = TO_CHAR(SYSDATE,'MON');
26. SELECT COUNT(*) FROM PROGRAMMER WHERE SEX = 'F';
27. SELECT DISTINCT(PROF1) FROM PROGRAMMER WHERE SEX = 'M';
28. SELECT AVG(SAL) FROM PROGRAMMER;
29. SELECT COUNT(*) FROM PROGRAMMER WHERE SAL BETWEEN 5000 AND 7500;
30. SELECT * FROM PROGRAMMER WHERE PROF1 NOT IN ('C','C++','PASCAL') AND PROF2 NOT IN ('C','C++','PASCAL');
31. SELECT PNAME,TITLE,SCOST FROM SOFTWARE WHERE SCOST IN (SELECT MAX(SCOST) FROM SOFTWARE GROUP BY PNAME);
32.SELECT 'Mr.' || PNAME || ' - has ' || TRUNC(MONTHS_BETWEEN(SYSDATE,DOJ)/12) || ' years of experience' “Programmer” FROM PROGRAMMER WHERE SEX = 'M' UNION SELECT 'Ms.' || PNAME || ' - has ' || TRUNC (MONTHS_BETWEEN (SYSDATE,DOJ)/12) || ' years of experience' “Programmer” FROM PROGRAMMER WHERE SEX = 'F';II . SCHEMA :
MGR is the empno of the employee whom the employee reports to. DEPTNO is a foreign key.QUERIES1. List all the employees who have at least one person reporting to them.2. List the employee details if and only if more than 10 employees are present in department no 10.3. List the name of the employees with their immediate higher authority.4. List all the employees who do not manage any one.5. List the employee details whose salary is greater than the lowest salary of an employee belonging to deptno 20. 6. List the details of the employee earning more than the highest paid manager.7. List the highest salary paid for each job.8. Find the most recently hired employee in each department.9. In which year did most people join the company? Display the year and the number of employees.
10. Which department has the highest annual remuneration bill?11. Write a query to display a ‘*’ against the row of the most recently hired employee.12. Write a correlated sub-query to list out the employees who earn more than the average salary of their department.13. Find the nth maximum salary.14. Select the duplicate records (Records, which are inserted, that already exist) in the EMP table.15. Write a query to list the length of service of the employees (of the form n years and m months).
KEYS:
1. SELECT DISTINCT(A.ENAME) FROM EMP A, EMP B WHERE A.EMPNO = B.MGR; or SELECT ENAME FROM EMP WHERE EMPNO IN (SELECT MGR FROM EMP);
2. SELECT * FROM EMP WHERE DEPTNO IN (SELECT DEPTNO FROM EMP GROUP BY DEPTNO HAVING COUNT(EMPNO)>10 AND DEPTNO=10);
3. SELECT A.ENAME "EMPLOYEE", B.ENAME "REPORTS TO" FROM EMP A, EMP B WHERE A.MGR=B.EMPNO;
4. SELECT * FROM EMP WHERE EMPNO IN ( SELECT EMPNO FROM EMP MINUS SELECT MGR FROM EMP);
5. SELECT * FROM EMP WHERE SAL > ( SELECT MIN(SAL) FROM EMP GROUP BY DEPTNO HAVING DEPTNO=20);
6. SELECT * FROM EMP WHERE SAL > ( SELECT MAX(SAL) FROM EMP GROUP BY JOB HAVING JOB = 'MANAGER' );
7. SELECT JOB, MAX(SAL) FROM EMP GROUP BY JOB;
8. SELECT * FROM EMP WHERE (DEPTNO, HIREDATE) IN (SELECT DEPTNO, MAX(HIREDATE) FROM EMP GROUP BY DEPTNO);
9. SELECT TO_CHAR(HIREDATE,'YYYY') "YEAR", COUNT(EMPNO) "NO. OF EMPLOYEES" FROM EMP GROUP BY TO_CHAR(HIREDATE,'YYYY') HAVING COUNT(EMPNO) = (SELECT MAX(COUNT(EMPNO)) FROM EMP GROUP BY TO_CHAR(HIREDATE,'YYYY'));
10. SELECT DEPTNO, LPAD(SUM(12*(SAL+NVL(COMM,0))),15) "COMPENSATION" FROM EMP GROUP BY DEPTNO HAVING SUM( 12*(SAL+NVL(COMM,0))) = (SELECT
MAX(SUM(12*(SAL+NVL(COMM,0)))) FROM EMP GROUP BY DEPTNO);
11. SELECT ENAME, HIREDATE, LPAD('*', "RECENTLY HIRED" FROM EMP WHERE HIREDATE = (SELECT MAX(HIREDATE) FROM EMP) UNION SELECT ENAME NAME, HIREDATE, LPAD(' ',15) "RECENTLY HIRED" FROM EMP WHERE HIREDATE != (SELECT MAX(HIREDATE) FROM EMP);
12. SELECT ENAME,SAL FROM EMP E WHERE SAL > (SELECT AVG(SAL) FROM EMP F WHERE E.DEPTNO = F.DEPTNO);
13. SELECT ENAME, SAL FROM EMP A WHERE &N = (SELECT COUNT (DISTINCT(SAL)) FROM EMP B WHERE A.SAL<=B.SAL);
14. SELECT * FROM EMP A WHERE A.EMPNO IN (SELECT EMPNO FROM EMP GROUP BY EMPNO HAVING COUNT(EMPNO)>1) AND A.ROWID!=MIN (ROWID));
15. SELECT ENAME "EMPLOYEE",TO_CHAR(TRUNC(MONTHS_BETWEEN(SYSDATE,HIREDATE)/12))||' YEARS '|| TO_CHAR(TRUNC(MOD(MONTHS_BETWEEN (SYSDATE, HIREDATE),12)))||' MONTHS ' "LENGTH OF SERVICE" FROM EMP;
OPERATING SYSTEM@@@@@@@@@@@@@@@@@@@
FAQ In Operating System
Following are a few basic questions that cover the essentials of OS:
1. When is a system in safe state?The set of dispatchable processes is in a safe state if there exists at least one temporal order in which all processes can be run to completion without resulting in a deadlock.
2. What is cycle stealing?We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at specific break points in an instruction cycle.
3. What is meant by arm-stickiness?If one or a few processes have a high access rate to data on one track of a storage disk, then they may monopolize the
device by repeated requests to that track. This generally happens with most common device scheduling algorithms (LIFO, SSTF, C-SCAN, etc). High-density multisurface disks are more likely to be affected by this than low density ones.
4. What are the stipulations of C2 level security?C2 level security provides for:> Discretionary Access Control> Identification and Authentication> Auditing> Resource reuse
5. What is busy waiting?The repeated execution of a loop of code while waiting for an event to occur is called busy-waiting. The CPU is not engaged in any real productive activity during this period, and the process does not progress toward completion.
6. What are short-, long- and medium-term scheduling?Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.
6. What are short-, long- and medium-term scheduling?Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.
7. What are turnaround time and response time?Turnaround time is the interval between the submission of a job and its completion. Response time is the interval between submission of a request, and the first response to that request.
8. What are the typical elements of a process image?
> User data: Modifiable part of user space. May include program data, user stack area, and programs that may be modified.> User program: The instructions to be executed.> System Stack: Each process has one or more LIFO stacks associated with it. Used to store parameters and calling addresses for procedure and system calls.> Process control Block (PCB): Info needed by the OS to control processes.
9. What is the Translation Lookaside Buffer (TLB)?In a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup. TLB contains those page-table entries that have been most recently used. Normally, each virtual memory reference causes 2 physical memory accesses-- one to fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit.
10. What is the resident set and working set of a process?Resident set is that portion of the process image that is actually in real-memory at a particular instant. Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques.)11. Explain the concept of Reentrancy.It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.Note: A reentrant procedure can be interrupted and called by an interrupting program, and still execute correctly on returning to the procedure.
12. Explain Belady's Anomaly.Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process' virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.
13. What is a binary semaphore? What is its use?A binary semaphore is one, which takes only 0 and 1 as values. They are used to implement mutual exclusion and synchronize concurrent processes.
14. What is thrashing?It is a phenomenon in virtual memory schemes when the processor spends most of its time swapping pages, rather than executing instructions. This is due to an inordinate number of page faults.
15. List the Coffman's conditions that lead to a deadlock.> Mutual Exclusion: Only one process may use a critical resource at a time.> Hold & Wait: A process may be allocated some resources while waiting for others.> No Pre-emption: No resource can be forcible removed from a process holding it.> Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain.16. Explain the popular multiprocessor thread-scheduling strategies.> Load Sharing: Processes are not assigned to a particular processor. A global queue of threads is maintained. Each processor, when idle, selects a thread from this queue. Note that load balancing refers to a scheme where work is allocated to processors on a more permanent basis.> Gang Scheduling: A set of related threads is scheduled to run on a set of processors at the same time, on a 1-to-1 basis. Closely related threads / processes may be scheduled this way to reduce synchronization blocking, and minimize process switching. Group scheduling predated this strategy.> Dedicated processor assignment: Provides implicit scheduling defined by assignment of threads to processors. For the duration of program execution, each program is allocated a set of processors equal in number to the number of threads in the program. Processors are chosen from the available pool.> Dynamic scheduling: The number of thread in a program can be altered during the course of execution.
17. When does the condition 'rendezvous' arise?In message passing, it is the condition in which, both, the sender and receiver are blocked until the message is delivered.
18. What is a trap and trapdoor?Trapdoor is a secret undocumented entry point into a program used to grant access without normal methods of access authentication. A trap is a software interrupt, usually the result of an error condition.
19. What are local and global page replacements?Local replacement means that an incoming page is brought in only to the relevant process' address space. Global replacement policy allows any page frame from any process to be replaced. The latter is applicable to variable partitions model only.
20. Define latency, transfer and seek time with respect to disk I/O.
Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time. 21. Describe the Buddy system of memory allocation.Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.
22. What is time-stamping?It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti<Tj or (b) if Ti=Tj and i<j.
23. How are the wait/signal operations for monitor different from those for semaphores?If a process in a monitor signal and no task is waiting on the condition variable, the signal is lost. So this allows easier program design. Whereas in semaphores, every operation affects the value of the semaphore, so the wait and signal operations should be perfectly balanced in the program.
24. In the context of memory management, what are placement and replacement algorithms?Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.
25. In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.
With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.25. In loading programs into memory, what is the difference between load-time dynamic linking and run-time dynamic linking?For load-time dynamic linking: Load module to be loaded is read into memory. Any reference to a target external module causes that module to be loaded and the references are updated to a relative address from the start base address of the application module.With run-time dynamic loading: Some of the linking is postponed until actual reference during execution. Then the correct module is loaded and linked.
26. What are demand- and pre-paging?With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.
27. Paging a memory management function, while multiprogramming a processor management function, are the two interdependent?Yes.
28. What is page cannibalizing?Page swapping or page replacements are called page cannibalizing.
29. What has triggered the need for multitasking in PCs?> Increased speed and memory capacity of microprocessors together with the support fir virtual memory and> Growth of client server computing
30. What are the four layers that Windows NT have in order to achieve independence?> Hardware abstraction layer> Kernel> Subsystems> System Services.
31. What is SMP?To achieve maximum efficiency and reliability a mode of operation known as symmetric multiprocessing is used. In essence, with SMP any process or threads can be assigned to any processor.32. What are the key object oriented concepts used by Windows NT?> Encapsulation> Object class and instance
33. Is Windows NT a full blown object oriented operating system? Give reasons.No Windows NT is not so, because its not implemented in object oriented language and the data structures reside within
one executive component and are not represented as objects and it does not support object oriented capabilities .
34. What is a drawback of MVT?It does not have the features like> ability to support multiple processors> virtual storage> source level debugging
35. What is process spawning?When the OS at the explicit request of another process creates a process, this action is called process spawning.
36. How many jobs can be run concurrently on MVT?15 jobs
37. List out some reasons for process termination.
> Normal completion> Time limit exceeded> Memory unavailable> Bounds violation> Protection error> Arithmetic error> Time overrun> I/O failure> Invalid instruction> Privileged instruction> Data misuse> Operator or OS intervention> Parent termination.38. What are the reasons for process suspension?> swapping> interactive user request> timing> parent process request
39. What is process migration?It is the transfer of sufficient amount of the state of process from one machine to the target machine
40. What is mutant?In Windows NT a mutant provides kernel mode or user mode mutual exclusion with the notion of ownership.
41. What is an idle thread?The special thread a dispatcher will execute when no ready thread is found.
42. What is FtDisk?It is a fault tolerance disk driver for Windows NT.
43. What are the possible threads a thread can have?> Ready> Standby> Running> Waiting> Transition
> Terminated.44. What are rings in Windows NT?Windows NT uses protection mechanism called rings provides by the process to implement separation between the user mode and kernel mode.
45. What is Executive in Windows NT?In Windows NT, executive refers to the operating system code that runs in kernel mode.
46. What are the sub-components of I/O manager in Windows NT?> Network redirector/ Server> Cache manager.> File systems> Network driver> Device driver
47. What are DDks? Name an operating system that includes this feature.DDks are device driver kits, which are equivalent to SDKs for writing device drivers. Windows NT includes DDks.
48. What level of security does Windows NT meets?C2 level security.
@------> C LANGUAGE@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@C is interviewer’s favorite language. If you have good command on C language you can get through Technical Interview easily. Most of the interviewers ask basic questions in C. Some times they may ask you to write small programs like reversal of a string, determining whether the given number is a palindrome or not and finding factorial of a given number using recursion etc. You should be able to write these programs quickly.
Most favorite question for interviewers is interchanging two variables with out using the third variable. Another favorite topic for interviewers is Pointers. Please go through pointers once before going to the interview.
Many interviewers look for logic in your program rather than syntax. Once you write the program you should be able to explain the logic to the interviewer with the help of flow-chart or algorithm. If there are more than one logic for a single program, choose the logic that is simple and easy to understand at the same time it should efficient one.
Below are around 100 FAQ in C language. Try to answer these questions on your own. I believe that if you are able to answer these questions, you can easily get through the technical interview.
1.What will be the output of the following code?
void main (){ int i = 0 , a[3] ;a[i] = i++;printf (“%d",a[i]) ;}Ans: The output for the above code would be a garbage value. In the statement a[i] = i++; the value of the variable i would get assigned first to a[i] i.e. a[0] and then the value of i would get incremented by 1. Since a[i] i.e. a[1] has not been initialized, a[i] will have a garbage value.
2. Why doesn't the following code give the desired result?
int x = 3000, y = 2000 ;long int z = x * y ;Ans: Here the multiplication is carried out between two ints x and y, and the result that would overflow would be truncated before being assigned to the variable z of type long int. However, to get the correct output, we should use an explicit cast to force long arithmetic as shown below:
long int z = ( long int ) x * y ;Note that ( long int )( x * y ) would not give the desired effect.
3.Why doesn't the following statement work?
char str[ ] = "Hello" ;strcat ( str, '!' ) ;Ans: The string function strcat( ) concatenates strings and not a character. The basic difference between a string and a character is that a string is a collection of characters, represented by an array of characters whereas a character is a single character. To make the above statement work writes the statement as shown below:strcat ( str, "!" ) ;
4. How do I know how many elements an array can hold?
Ans: The amount of memory an array can consume depends on the data type of an array. In DOS environment, the amount of memory an array can consume depends on the current memory model (i.e. Tiny, Small, Large, Huge, etc.). In general an array cannot consume more than 64 kb. Consider following program, which shows the maximum number of elements an array of type int, float and char can have in case of Small memory model.main( ){int i[32767] ;float f[16383] ;char s[65535] ;}
5. How do I write code that reads data at memory location specified by segment and offset?
Ans: Use peekb( ) function. This function returns byte(s) read from specific segment and offset locations in memory. The following program illustrates use of this function. In this program from VDU memory we have read characters and its attributes of the first row. The information stored in file is then further read and displayed using peek( ) function.
6. How do I compare character data stored at two different memory locations?
Ans: Sometimes in a program we require to compare memory ranges containing strings. In such a situation we can use functions like memcmp( ) or memicmp( ). The basic difference between two functions is that memcmp( ) does a case-sensitive comparison whereas memicmp( ) ignores case of characters. Following program illustrates the use of both the functions.
#include <mem.h>main( ){char *arr1 = "Kicit" ;
char *arr2 = "kicitNagpur" ;int c ;c = memcmp ( arr1, arr2, sizeof ( arr1 ) ) ;if ( c == 0 )printf ( "\nStrings arr1 and arr2 compared using memcmp are identical" ) ;elseprintf ( "\nStrings arr1 and arr2 compared using memcmp are not identical") ;
c = memicmp ( arr1, arr2, sizeof ( arr1 ) ) ;if ( c == 0 )printf ( "\nStrings arr1 and arr2 compared using memicmp are identical" );elseprintf ( "\nStrings arr1 and arr2 compared using memicmp are notidentical" ) ;}
7. Fixed-size objects are more appropriate as compared to variable size data objects. Using variable-size data objects saves very little space. Variable size data objects usually have some overhead. Manipulation of fixed-size data objects is usually faster and easier. Use fixed size when maximum size is clearly bounded and close to average. And use variable-size data objects when a few of the data items are bigger than the average size. For example,
The first form uses variable-size data objects. It allocates 10 pointers, which are pointing to 10 string constants of variable size. Assuming each pointer is of 4 bytes, it requires 90 bytes. On the other hand, the second form uses fixed size data objects. It allocates 10 arrays of 6 characters each. It requires only 60 bytes of space. So, the variable-size in this case does not offer any advantage over fixed size.
8. The Spawnl( ) function...
DOS is a single tasking operating system, thus only one program runs at a time. The Spawnl( ) function provides us with the capability of starting the execution of one program from within another program. The first program is called the parent process and the second program that gets called from within the first program is called a child process. Once the second program starts execution, the first is put on hold until the second program completes execution. The first program
is then restarted. The following program demonstrates use of spawnl( ) function.
/* Mult.c */
int main ( int argc, char* argv[ ] ){int a[3], i, ret ;if ( argc < 3 || argc > 3 ){printf ( "Too many or Too few arguments..." ) ;exit ( 0 ) ;}
for ( i = 1 ; i < argc ; i++ )a[i] = atoi ( argv[i] ) ;ret = a[1] * a[2] ;return ret ;}
main( ){int val ;val = spawnl ( P_WAIT, "C:\\Mult.exe", "3", "10","20", NULL ) ;printf ( "\nReturned value is: %d", val ) ;}
Here, there are two programs. The program 'Mult.exe' works as a child process whereas 'Spawn.exe' works as a parent process. On execution of 'Spawn.exe' it invokes 'Mult.exe' and passes the command-line arguments to it. 'Mult.exe' in turn on execution, calculates the product of 10 and 20 and returns the value to val in 'Spawn.exe'. In our call to spawnl( ) function, we have passed 6 parameters, P_WAIT as the mode of execution, path of '.exe' file to run as child process, total number of arguments to be passed to the child process, list of command line arguments and NULL. P_WAIT will cause our application to freeze execution until the child process has completed its execution. This parameter needs to be passed as the default parameter if you are working under DOS. under other operating systems that support multitasking, this parameter can be P_NOWAIT or P_OVERLAY. P_NOWAIT will cause the parent process to execute along with the child process, P_OVERLAY will load the child process on top of the parent process in the memory.-------------------------------------------------------------------------------------------------9.
Are the following two statements identical?
char str[6] = "Kicit" ;
char *str = "Kicit" ;Ans: No! Arrays are not pointers. An array is a single, pre-allocated chunk of contiguous elements (all of the same type), fixed in size and location. A pointer on the other hand, is a reference to any data element (of a particular type) located anywhere. A pointer must be assigned to point to space allocated elsewhere, but it can be reassigned any time. The array declaration char str[6] ; requests that space for 6 characters be set aside, to be knownby name str. In other words there is a location named str at which six characters are stored. The pointer declaration char *str ; on the other hand, requests a place that holds a pointer, to be known by the name str. This pointer can point almost anywhere to any char, to any contiguous array of chars, or nowhere.-------------------------------------------------------------------------------------------------10.
Is the following code fragment correct?
const int x = 10 ;int arr[x] ;Ans: No! Here, the variable x is first declared as an int so memory is reserved for it. Then it is qualified by a const qualifier. Hence, const qualified object is not a constant fully. It is an object with read only attribute, and in C, an object associated with memory cannot be used in array dimensions.
11.
How do I write code to retrieve current date and time from the system and display it as a string?
Ans: Use time( ) function to get current date and time and then ctime( ) function to display it as a string. This is shown in following code snippet.
#include <sys\types.h>
void main( ){time_t curtime ;char ctm[50] ;
time ( &curtime ) ; //retrieves current time &stores in curtimeprintf ( "\nCurrent Date & Time: %s", ctime (&curtime ) ) ;}
How do I change the type of cursor and hide a cursor?
Ans: We can change the cursor type by using function _setcursortype( ). This function can change the cursor type to solid cursor and can even hide a cursor. Following code shows how to change the cursor type and hide cursor.
/* Change cursor to a solid cursor */_setcursortype ( _SOLIDCURSOR ) ;
/* Change back to the normal cursor */_setcursortype ( _NORMALCURSOR ) ;}-------------------------------------------------------------------------------------------------13.
How do I write code that would get error number and display error message if any standard error occurs?
main( ){char *errmsg ;FILE *fp ;fp = fopen ( "C:\file.txt", "r" ) ;if ( fp == NULL ){errmsg = strerror ( errno ) ;printf ( "\n%s", errmsg ) ;}}Here, we are trying to open 'file.txt' file. However, if the file does not exist, then it would cause an error. As a result, a value (in this case 2) related to the error generated would get set in errno. errno is an external int variable declared in 'stdlib.h' and also in 'errno.h'. Next, we have called sterror( ) function which takes an error number and returns a pointer to standard error message related to the given error number.-------------------------------------------------------------------------------------------------14.
How do I write code to get the current drive as well as set the current drive?
Ans: The function getdisk( ) returns the drive number of current drive. The drive number 0 indicates 'A' as the current drive, 1 as 'B' and so on. The Setdisk( ) function sets the current drive. This function takes one argument which is an integer indicating the drive to be set. Following program demonstrates use of both the functions.
#include <dir.h>
main( ){int dno, maxdr ;
dno = getdisk( ) ;printf ( "\nThe current drive is: %c\n", 65 + dno) ;
maxdr = setdisk ( 3 ) ;dno = getdisk( ) ;printf ( "\nNow the current drive is: %c\n", 65 +dno ) ;}-------------------------------------------------------------------------------------------------15.
The functions memcmp( ) and memicmp( )
The functions memcmp( ) and memicmp( ) compares first n bytes of given two blocks of memory or strings. However, memcmp( ) performs comparison as unsigned chars whereas memicmp( ) performs comparison as chars but ignores case (i.e. upper or lower case). Both the functions return an integer value where 0 indicates that two memory buffers compared are identical. If the value returned is greater than 0 then it indicates that the first buffer is bigger than the second one. The value less than 0 indicate that the first buffer is less than the second buffer. The following code snippet demonstrates use of both
show ( int r ){if ( r == 0 )printf ( "\nThe buffer str1 and str2 holdidentical data" ) ;if ( r > 0 )printf ( "\nThe buffer str1 is bigger than bufferstr2" ) ;if ( r < 0 )printf ( "\nThe buffer str1 is less than bufferstr2" ) ;}-------------------------------------------------------------------------------------------------
16.
How do I write code to find an amount of free disk space available on current drive?
Ans: Use getdfree( ) function as shown in follow code.
if ( disk.df_sclus == 0xFFFF ){printf ( "\ngetdfree( ) function failed\n");exit ( 1 ) ;}
freesp = ( long ) disk.df_avail* ( long ) disk.df_bsec* ( long ) disk.df_sclus ;printf ( "\nThe current drive %c: has %ld bytesavailable as free space\n", 'A' + dr, freesp ) ;}
17.
Use of array indices...If we wish to store a character in a char variable ch and the character to be stored depends on the value of another
variable say color (of type int), then the code would be as shown below:
switch ( color ){case 0 :ch = 'R' ;break ;case 1 :ch = 'G' ;break ;case 2 :ch = 'B' ;break ;}In place of switch-case we can make use of the value in color as an index for a character array. How to do this is shown in following code snippet.
char *str = "RGB' ;char ch ;int color ;// codech = str[ color ] ;-------------------------------------------------------------------------------------------------18.
Function atexit( ) recevies parameter as the address of function of the type void fun ( void ). The function whose address is passed to atexit( ) gets called before the termination of program. If atexit( ) is called for more than one function then the functions are called in "first in last out" order. You can verify that from the output.
Ans: The malloc( ) / free( ) implementation remembers the size of each block allocated and returned, so it is not necessary to remind it of the size when freeing.-------------------------------------------------------------------------------------------------21.
What is the use of randomize( ) and srand( ) function?
Ans: While generating random numbers in a program, sometimes we require to control the series of numbers that random number generator creates. The process of assigning the random number generators starting number is called seeding the generator. The randomize( ) and srand( ) functions are used to seed the random number generators. The randomize( ) function uses PC's clock to produce a random seed, whereas the srand( ) function allows us to specify the random number generator's starting value.
How do I determine amount of memory currently available for allocating?
Ans: We can use function coreleft( ) to get the amount of memory available for allocation. However, this function does not give an exact amount of unused memory. If, we are
using a small memory model, coreleft( ) returns the amount of unused memory between the top of the heap and stack. If we are using a larger model, this function returns the amount of memory between the highest allocated memory and the end of conventional memory. The function returns amount of memory in terms of bytes.
How does a C program come to know about command line arguments?
Ans: When we execute our C program, operating system loads the program into memory. In case of DOS, it first loads 256 bytes into memory, called program segment prefix. This contains file table, environment segment, and command line information. When we compile the C program the compiler inserts additional code that parses the command, assigning it to the argv array, making the arguments easily accessible within our C program.24.
When we open a file, how does functions like fread( )/fwrite( ), etc. get to know from where to read or to write the data?
Ans: When we open a file for read/write operation using function like fopen( ), it returns a pointer to the structure of type FILE. This structure stores the file pointer called position pointer, which keeps track of current location within the file. On opening file for read/write operation, the file pointer is set to the start of the file. Each time we read/write a character, the position pointer advances one character. If we read one line of text at a step from the file, then file pointer advances to the start of the next line. If the file is opened in append mode, the file pointer is placed at the very end of the file. Using fseek( ) function we can set the file pointer to some other place within the file.-------------------------------------------------------------------------------------------------
25.
The sizeof( ) function doesn’t return the size of the block of memory pointed to by a pointer. Why?
Ans: The sizeof( ) operator does not know that malloc( ) has been used to allocate a pointer. sizeof( ) gives us the size of pointer itself. There is no handy way to find out the size of a block allocated by malloc( ).-------------------------------------------------------------------------------------------------26.FP_SEG And FP_OFF…
Sometimes while working with far pointers we need to break a far address into its segment and offset. In such situations we can use FP_SEG and FP_OFF macros. Following program illustrates the use of these two macros.#include <dos.h>
main( ){unsigned s, o ;char far *ptr = "Hello!" ;
s = FP_SEG ( ptr ) ;o = FP_OFF ( ptr ) ;printf ( "\n%u %u", s, o ) ;}
How do I write a program to convert a string containing number in a hexadecimal form to its equivalent decimal?Ans: The following program demonstrates this:main( ){char str[] = "0AB" ;int h, hex, i, n ;n = 0 ; h = 1 ;for ( i = 0 ; h == 1 ; i++ ){if ( str[i] >= '0' && str[i] <= '9' )hex = str[i] - '0' ;else{if ( str[i] >= 'a' && str[i] <= 'f' )hex = str[i] - 'a' + 10 ;elseif ( str[i] >= 'A' && str[i] <= 'F' )hex = str[i] - 'A' + 10 ;elseh = 0 ;}if ( h == 1 )n = 16 * n + hex ;}printf ( "\nThe decimal equivalent of %s is %d",str, n ) ;}The output of this program would be the decimal equivalent of 0AB is 171.-------------------------------------------------------------------------------------------------28.
How do I write code that reads the segment register settings?
Ans: We can use segread( ) function to read segment register settings. There are four segment registers—code segment,
data segment, stack segment and extra segment. Sometimes when we use DOS and BIOS services in a program we need to know the segment register's value. In such a situation we can use segread( ) function. The following program illustrates the use of this function.#include <dos.h>main( ){struct SREGS s ;segread ( &s ) ;printf ( "\nCS: %X DS: %X SS: %X ES: %X",s.cs,s.ds, s.ss, s.es ) ;}-------------------------------------------------------------------------------------------------29.
What is environment and how do I get environment for a specific entry?
Ans: While working in DOS, it stores information in a memory region called environment. In this region we can place configuration settings such as command path, system prompt, etc. Sometimes in a program we need to access the information contained in environment. The function getenv( ) can be used when we want to access environment for a specific entry. Following program demonstrates the use of this function.#include <stdio.h>#include <stdlib.h>
printf ( "\n%s", str ) ;}Here we have called time( ) function which returns current time. This time is returned in terms of seconds, elapsed since 00:00:00 GMT, January 1, 1970. To extract the week day, day of month, etc. from this value we need to break down the value to a tm structure. This is done by the function localtime( ). Then we have called strftime( ) function to format the time and store it in a string str.
31.
If we have declared an array as global in one file and we are using it in another file then why doesn't the sizeof operator works on an extern array?
Ans: An extern array is of incomplete type as it does not contain the size. Hence we cannot use sizeof operator, as it cannot get the size of the array declared in another file. To resolve this use any of one the following two solutions:1. In the same file declare one more variable that holds the size of array. For example,
array.c
int arr[5] ;int arrsz = sizeof ( arr ) ;
myprog.c
extern int arr[] ;extern int arrsz ;2. Define a macro which can be used in an arraydeclaration. For example,
How do I write printf( ) so that the width of a field can be specified at runtime?
Ans: This is shown in following code snippet.
main( ){int w, no ;printf ( "Enter number and the width for thenumber field:" ) ;scanf ( "%d%d", &no, &w ) ;printf ( "%*d", w, no ) ;}Here, an '*' in the format specifier in printf( ) indicates that an int value from the argument list should be used for the field width.-------------------------------------------------------------------------------------------------33.
How to find the row and column dimension of a given 2-D array?
Ans: Whenever we initialize a 2-D array at the same place where it has been declared, it is not necessary to mention the row dimension of an array. The row and column dimensions of such an array can be determined programmatically as shown in following program.
int c = sizeof ( a[0] ) / sizeof ( int ) ;int r = ( sizeof ( a ) / sizeof ( int ) ) / c ;int i, j ;
printf ( "\nRow: %d\nCol: %d\n", r, c ) ;for ( i = 0 ; i < r ; i++ ){for ( j = 0 ; j < c ; j++ )printf ( "%d ", a[i][j] ) ;printf ( "\n" ) ;}}-------------------------------------------------------------------------------------------------34.
The access( ) function...
The access( ) function checks for the existence of a file and also determines whether it can be read, written to or executed. This function takes two arguments the filename and an integer indicating the access mode. The values 6, 4, 2, and 1 checks for read/write, read, write and execute permission of a given file, whereas value 0 checks whether the file exists or not. Following program demonstrates how we can use access( ) function to check if a given file exists.
#include <io.h>
main( ){char fname[67] ;
printf ( "\nEnter name of file to open" ) ;gets ( fname ) ;
if ( access ( fname, 0 ) != 0 ){printf ( "\nFile does not exist." ) ;return ;}}
no = 14.3216 ;gcvt ( no, dg, str ) ;printf ( "String: %s\n", str ) ;}
36.What is a stack ?
Ans: The stack is a region of memory within which our programs temporarily store data as they execute. For example, when a program passes parameters to functions, C places the parameters on the stack. When the function completes, C removes the items from the stack. Similarly, when a function declares local variables, C stores the variable's values on the stack during the function's execution.
Depending on the program's use of functions and parameters, the amount of stack space that a program requires will differ.-------------------------------------------------------------------------------------------------37.Allocating memory for a 3-D array
#include "alloc.h"#define MAXX 3#define MAXY 4#define MAXZ 5main( ){int ***p, i, j, k ;p = ( int *** ) malloc ( MAXX * sizeof ( int ** ) ) ;for ( i = 0 ; i < MAXX ; i++ ){p[i] = ( int ** ) malloc ( MAXY * sizeof ( int * ) ) ;for ( j = 0 ; j < MAXY ; j++ )p[i][j] = ( int * ) malloc ( MAXZ * sizeof ( int ) ) ;}for ( k = 0 ; k < MAXZ ; k++ ){for ( i = 0 ; i < MAXX ; i++ ){for ( j = 0 ; j < MAXY ; j++ ){p[i][j][k] = i + j + k ;printf ( "%d ", p[i][j][k] ) ;}printf ( "\n" ) ;}printf ( "\n\n" ) ;}}Data StructuresHow to distinguish between a binary tree and a tree?
Ans: A node in a tree can have any number of branches. While a binary tree is a tree structure in which any node can have at most two branches. For binary trees we distinguish between the subtree on the left and subtree on the right, whereas for trees the order of the subtrees is irrelevant.Consider the following figure...
This above figure shows two binary trees, but these binary trees are different. The first has an empty right subtree while the second has an empty left subtree. If the above are regarded as trees (not the binary trees), then they are same despite the fact that they are drawn differently. Also, an empty binary tree can exist, but there is no tree having zero nodes.-------------------------------------------------------------------------------------------------38.How do I use the function ldexp( ) in a program?
Ans: The math function ldexp( ) is used while solving the complex mathematical equations. This function takes two arguments, a double value and an int respectively. The order in which ldexp( ) function performs calculations is ( n * pow ( 2, exp ) ) where n is the double value and exp is the integer. The following program demonstrates the use of this function.
#include <stdio.h>#include <math.h>
void main( ){double ans ;double n = 4 ;
ans = ldexp ( n, 2 ) ;printf ( "\nThe ldexp value is : %lf\n", ans ) ;}Here, ldexp( ) function would get expanded as ( 4 * 2 * 2 ), and the output would be the ldexp value is : 16.000000-------------------------------------------------------------------------------------------------
39.Can we get the mantissa and exponent form of a given number?
Ans: The function frexp( ) splits the given number into a mantissa and exponent form. The function takes two arguments, the number to be converted as a double value and an int to store the exponent form. The function returns the mantissa part as a double value. Following example demonstrates the use of this function.
#include <math.h>#include <stdio.h>
void main( ){double mantissa, number ;int exponent ;
How do I write code that executes certain function only at program termination?Ans: Use atexit( ) function as shown in following program.
#include <stdlib.h>main( ){int ch ;void fun ( void ) ;atexit ( fun ) ;// code}void fun( void ){printf ( "\nTerminate program......" ) ;getch( ) ;}-------------------------------------------------------------------------------------------------41.What are memory models?Ans: The compiler uses a memory model to determine how much memory is allocated to the program. The PC divides memory into blocks called segments of size 64 KB. Usually, program uses one segment for code and a second segment for data. A memory model defines the number of segments the compiler can use for each. It is important to know which memory model can be used for a program. If we use wrong memory model, the program might not have enough memory to execute. The problem can be solved using larger memory model. However, larger the memory model, slower is your program execution. So we must choose the smallest memory model that satisfies our program needs. Most of the compilers support memory models like tiny, small, medium, compact, large and huge.
42.How does C compiler store elements in a multi-dimensional array?
Ans: The compiler maps multi-dimensional arrays in two ways—Row major order and Column order. When the compiler places elements in columns of an array first then it is called column-major order. When the compiler places elements in rows of an array first then it is called row-major order. C compilers store multidimensional arrays in row-major order. For example, if there is a multi-dimensional array a[2][3], then according row-major order, the elements would get stored in memory following order:a[0][0], a[0][1], a[0][2], a[1][0], a[1][1], a[1][2]-------------------------------------------------------------------------------------------------43.
If the result of an _expression has to be stored to one of two variables, depending on a condition, can we use conditional operators as shown below?
( ( i < 10 ) ? j : k ) = l * 2 + p ;Ans: No! The above statement is invalid. We cannot use the conditional operators in this fashion. The conditional
operators like most operators, yields a value, and we cannot assign the value of an _expression to a value. However, we can use conditional operators as shown in following code snippet.
main( ){int i, j, k, l ;i = 5 ; j = 10 ; k = 12, l = 1 ;* ( ( i < 10 ) ? &j : &k ) = l * 2 + 14 ;printf ( "i = %d j = %d k = %d l = %d", i, j, k, l ) ;}
The output of the above program would be as given below:i = 5 j = 16 k = 12 l = 1-------------------------------------------------------------------------------------------------44.
How can I find the day of the week of a given date?
Ans: The following code snippet shows how to get the day of week from the given date.
dayofweek ( int yy, int mm, int dd ){/*Monday = 1 and Sunday = 0 *//* month number >= 1 and <= 12, yy > 1752 or so */static int arr[ ] = { 0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4 } ;yy = yy - mm < 3 ;return ( yy + yy / 4 - yy / 100 + yy / 400 + arr[ mm - 1] + dd ) % 7 ;}
What's the difference between these two declarations?
struct str1 { ... } ;typedef struct { ... } str2 ;Ans : The first form declares a structure tag whereas the second declares a typedef. The main difference is that the second declaration is of a slightly more abstract type -- its users don't necessarily know that it is a structure, and the keyword struct is not used when declaring instances of it.
How do I print the contents of environment variables?
Ans:. The following program shows how to achieve this:main( int argc, char *argv[ ], char *env[ ] ){int i = 0 ;clrscr( ) ;while ( env[ i ] )printf ( "\n%s", env[ i++ ] ) ;}
main( ) has the third command line argument env, which is an array of pointers to the strings. Each pointer points to an environment variable from the list of environment variables.-------------------------------------------------------------------------------------------------47.div( )...
The function div( ) divides two integers and returns the quotient and remainder. This function takes two integer values as arguments; divides first integer with the second one and returns the answer of division of type div_t. The data type div_t is a structure that contains two long ints, namely quot and rem, which store quotient and remainder of division respectively. The following example shows the use of div( ) function.
#include <stdlib.h>void main( ){div_t res ;
res = div ( 32, 5 ) ;printf ( "\nThe quotient = %d and remainder = %d ", res.quot, res.rem ) ;}48.What would the second and the third printf( ) output the following program?
Ans: For the above given program, we expect the output as Good Evening and Good Afternoon, for the second and third printf( ). However, the output would be as shown below.
First string = Good MorningGood EveningGood AfternoonSecond string = ( null )Third string =
What is missing in the above given code snippet is a comma separator which should separate the strings Good Morning, Good Evening and Good Afternoon. On adding comma, we would get the output as shown below.
First string = Good MorningSecond string = Good EveningThird string = Good Afternoon-------------------------------------------------------------------------------------------------49.
How do I use scanf( ) to read the date in the form 'dd-mm-yy' ?Ans: There are two ways to read the date in the form of 'dd-mm-yy' one possible way is...
int dd, mm, yy ;char ch ; /* for char '-' */printf ( "\nEnter the date in the form of dd-mm-yy : " ) ;scanf( "%d%c%d%c%d", &dd, &ch, &mm, &ch, &yy ) ;
And another best way is to use suppression character * as...
int dd, mm, yy ;scanf( "%d%*c%d%*c%d", &dd, &mm, &yy ) ;
The suppression character * suppresses the input read from the standard input buffer for the assigned control character.-------------------------------------------------------------------------------------------------50.
How do I print a floating-point number with higher precision say 23.34568734 with only precision up to two decimal places?
Ans: This can be achieved through the use of suppression char '*' in the format string of printf( ) as shown in the following program.main( ){int i = 2 ;float f = 23.34568734 ;printf ( "%.*f", i, f ) ;}The output of the above program would be 23.35.
Ans: No. *ptr++ increments the pointer and not the value pointed by it, whereas ++*ptr increments the value being pointed to by ptr.-------------------------------------------------------------------------------------------------
52.strpbrk( )
The function strpbrk( ) takes two strings as parameters. It scans the first string, to find, the first occurrence of any character appearing in the second string. The function returns a pointer to the first occurrence of the character it found in the first string. The following program demonstrates the use of string function strpbrk( ).
if ( p )printf ( "The first character found in str1 is %c", *p ) ;elseprintf ( "The character not found" ) ;}The output of the above program would be the first character found in str1 is e
53.
Can we convert an unsigned long integer value to a string?
Ans: The function ultoa( ) can be used to convert an unsigned long integer value to a string. This function takes three arguments, first the value that is to be converted, second the base address of the buffer in which the converted number has to be stored (with a string terminating null character '\0') and the last argument specifies the base to be used in converting the value. Following example demonstrates the use of this function.
#include <stdlib.h>void main( ){unsigned long ul = 3234567231L ;char str[25] ;
ultoa ( ul, str, 10 ) ;printf ( "str = %s unsigned long = %lu\n", str, ul ) ;}
-------------------------------------------------------------------------------------------------54.ceil( ) and floor( )
The math function ceil( ) takes a double value as an argument. This function finds the smallest possible integer to which the given number can be rounded up. Similarly, floor( ) being a math function, takes a double value as an argument and returns the largest possible integer to which the given double value can be rounded down. The following program demonstrates the use of both the functions.
#include <math.h>void main( ){double no = 1437.23167 ;double down, up ;
down = floor ( no ) ;up = ceil ( no ) ;
printf ( "The original number %7.5lf\n", no ) ;printf ( "The number rounded down %7.5lf\n", down ) ;printf ( "The number rounded up %7.5lf\n", up ) ;}
The output of this program would be,The original number 1437.23167The number rounded down 1437.00000The number rounded up 1438.00000-------------------------------------------------------------------------------------------------55.
How do I use function ecvt( ) in a program?
Ans: The function ecvt( ) converts a floating-point value to a null terminated string. This function takes four arguments, such as, the value to be converted to string, the number of digits to be converted to string, and two integer pointers. The two-integer pointer stores the position of the decimal point (relative to the string) and the sign of the number, respectively. If the value in a variable, used to store sign is 0, then the number is positive and, if it is non-zero, then the number is negative. The function returns a pointer to the string containing digits. Following program demonstrates the use of this function.
If we run the executable file of this program at command prompt passing the command line arguments as follows:
> mydir abc.c /s
This will search the file 'abc.c' in the current directory.-------------------------------------------------------------------------------------------------57.
Suppose I have a structure having fields name, age, salary and have passed address of age to a function fun( ). How I
can access the other member of the structure using the address of age?Ans:struct emp{char name[20] ;int age ;float salary ;} ;main( ){struct emp e ;printf ( "\nEnter name: " ) ;scanf ( "%s", e.name ) ;printf ( "\nEnter age: " ) ;scanf ( "%d", &e.age ) ;printf ( "\nEnter salary: " ) ;scanf ( "%f", &e.salary ) ;fun ( &e.age ) ;}fun ( int *p ){struct emp *q ;int offset ;offset = ( char * ) ( & ( ( struct emp * ) 0 ) -> age ) - ( char * ) ( (struct emp* ) 0 ) ;q = ( struct emp * ) ( ( char * ) p - offset ) ;printf ( "\nname: %s", q -> name ) ;printf ( "\nage: %d", q -> age ) ;printf ( "\nsalary: %f", q -> salary ) ;}
58.
How to restrict the program's output to a specific screen region?
Ans: A C function window( ) can be used to restrict the screen output to a specific region. The window( ) function defines a text-mode window. The parameters passed to this function defines the upper-left and lower-right corner of the region within which you want the output. In the following program, the string 'Hello!' gets printed within the specified region. To print the string we must use cprintf( ) function which prints directly on the text-mode window.
Sometimes you need to prompt the user for a password. When the user types in the password, the characters the user enters should not appear on the screen. A standard library function getpass( ) can be used to perform such function. Maximum number of characters that can be entered as password is 8.
main( ){char *pwd ;
pwd = getpass ( "Enter Password" ) ;
if ( strcmp ( pwd, "orgcity" ) )printf ( "\nPassword %s is incorrect", pwd ) ;elseprintf ( "\nCorrect Password" ) ;}-------------------------------------------------------------------------------------------------60.How to obtain the current drive through C ?
Ans: We can use the function _getdrive( ) to obtain the current drive. The _getdrive( ) function uses DOS function 0X19 to get the current drive number
#include <direct.h>main( ){int disk ;disk = _getdrive( ) + 'A' - 1 ;printf ( "The current drive is: %c\n", disk ) ;}-------------------------------------------------------------------------------------------------61.
How come the output for both the programs is different when the logic is same?
main( ){int i, j ;
for ( i = 1, j = 1 ; i <= 5, j <= 100 ; i++, j++ ){gotoxy ( 1, 1, ) ;printf ( "%d %d", i, j ) ;}}
main( ){
int i, j ;
for ( i =1, j = 1; j <= 100, i <= 5; i++, j++ ){gotoxy ( 1, 1 ) ;printf ( "%d %d", i, j ) ;}}
Output -> 5 5Even if logic of both the programs is same the output of the first program comes out to be 100, 100, but of the second program it is 5, 5. The comma operator plays a vital role inside the for loop. It always considers the value of the latest variable. So, at the time of testing the condition in for loop, the value of j will be considered in the first program and value of i in the second.-------------------------------------------------------------------------------------------------62.Can we get the x and y coordinate of the current cursor position ?
Ans : The function wherex( ) and wherey( ) returns the x-coordinate and y-coordinate of the current cursor position respectively. Both the functions return an integer value. The value returned by wherex( ) is the horizontal position of cursor and the value returned by wherey( ) is the vertical position of the cursor. Following program shows how to use the wherex( ) and wherey( ) functions.
63.How do I programmatically delete lines in the text window?
Ans: While writing programs that perform screen-based I/O, you may want to-delete the current line's contents, moving one line up, all of the output that follows. In such cases a function called delline( ) can be used. Following code snippet illustrates the use of function delline( ).
#include <conio.h>main( ){int i ;clrscr( ) ;
for ( i = 0; i <= 23; i++ )printf ( "Line %d\r\n", i ) ;
printf ( "Press a key to continue : " ) ;getch( ) ;
How do I get the time elapsed between two function calls ?
Ans: The function difftime( ) finds the difference between two times. It calculates the elapsed time in seconds and returns the difference between two times as a double value.
main( ){int a[] = { 2, -34, 56, 78, 112, 33, -7, 11, 45, 29, 6 } ;int s ;time_t t1, t2 ; // time_t defines the value used for time function
s = sizeof ( a ) / 2 ;t1 = time ( NULL ) ;sel_sort ( a, s ) ; // sort array by selection sortbub_sort ( a, s ) ; // sort array by bubble sort methodt2 = time ( NULL ) ;printf ( "\nThe difference between two function calls is %f", difftime (t2, t1 ) ) ;}
In the above program we have called difftime( ) function that returns the time elapsed from t1 to t2.-------------------------------------------------------------------------------------------------65.
How do I use swab( ) in my program ?
Ans: The function swab( ) swaps the adjacent bytes of memory. It copies the bytes from source string to the target string, provided that the number of characters in the source string is even. While copying, it swaps the bytes which are then assigned to the target string.
Turbo C provides various command line compiler options which we can use through TCC. The compiler options include : displaying specific warning messages, generating 8087 hardware instructions, using a filename for generating assembly code, etc. Instead of compiler options being executed at command line we can use these compiler options in our program. This can be achieved using #pragma options. We can use various flags with #pragma options to use the compiler options. All these flags are available in turbo C's online help.-------------------------------------------------------------------------------------------------67.
I have an array declared in file 'F1.C' as,int a[ ] = { 1, 2, 3, 4, 5, 6 } ;and used in the file 'F2.C' as,extern int a[ ] ;
In the file F2.C, why sizeof doesn't work on the array a[ ]?
Ans: An extern array of unspecified size is an incomplete type. You cannot apply sizeof to it, because sizeof operates during compile time and it is unable to learn the size of an array that is defined in another file. You have three ways to resolve this problem:1. In file 'F1.C' define as,int a[ ] = { 1, 2, 3, 4, 5, 6 } ;int size_a = sizeof ( a ) ;and in file F2.C declare as,extern int a[ ] ;extern int size_a ;
extern int a[ ] ;Here the element -1 is used as a sentinel value, so the code canunderstand the end without any explicit size.
68.
How to delete a line from text displayed on the screen?
Ans: Sometimes, specially when we are creating a text editor like program we may wish to allow user to delete a line. We can do so by using two functions namely clreol( ) and delline( ). The clreol( ) function deletes the line from the current cursor position to the end of line. The delline() function deletes the entire line at the current cursor position andmoves up the following line. Following program shows how to use these functions.
#include <conio.h>
main( ){int i ;
for ( i = 1 ; i <= 20 ; i++ )printf ( "This is Line %d\n", i ) ;
getch( ) ;gotoxy ( 1, 7 ) ;clreol( ) ;
getch( ) ;gotoxy ( 1, 12 ) ;delline( ) ;
getch( ) ;}-------------------------------------------------------------------------------------------------69.How do I programmatically insert lines in the text window?
Ans: We can insert a blank line in the text window using the insline( ) function. This function inserts line at current cursor position. While doing so, it shifts down the lines that are below the newly inserted line.
#include <conio.h>void main( ){
printf ( "The little snail was slowly moving up. She wanted\r\n" ) ;printf ( "to reach the top of the tree. It was chilly\r\n" ) ;printf ( "winter season. Most of the animals were resting in\r\n" ) ;printf ( "their nests as there was a heavy snow fall.\r\n" ) ;printf ( "\r\nPress any key to continue:" ) ;
for ( i = 0 ; i < 16 ; i++ )printf ( "%d", ( num << i & 1 << 15 ) ? 1 : 0 ) ;}
Ans: The output of this program is the binary equivalent of the given number. We have used bitwise operators to get the binary number.-------------------------------------------------------------------------------------------------71.Graphics
Building Mouse Cursors...
In text mode the mouse cursor appears as a block, whereas in graphics mode it appears as an arrow. If we wish we can change the graphics cursor to any other shape the way Windows does. The mouse cursor in graphics mode occupies a 16 by 16 pixel box. By highlighting or dehighlighting some of the pixels in this box we can get the desired shape. For example, the following bit-pattern can be used to generate the cursor which looks like an hour-glass.1111111111111111 00000000000000001000000000000001 00000000000000001111111111111111 00000000000000001000000000000001 00000000000000000100000000000010 10000000000000010010000000000100 11000000000000110000100000010000 11110000000011110000001001000000 1111110000111111
0000001001000000 11111100001111110000100000010000 11110000000011110010000000000100 11000000000000110100000000000010 10000000000000011000000000000001 00000000000000001111111111111111 00000000000000001000000000000001 00000000000000001111111111111111 0000000000000000Mouse pointer bitmap Screen Mask the one's in the mouse pointer bitmap indicate that the pixel would be drawn whereas the zeros indicate that the pixel would stand erased. It is important to note that the mouse pointer bit pattern is 32 bytes long. However, while actually writing a program to change the pointer shape we need a 64 byte bit-map. This provision is made to ensure that when the cursor reaches a position on the screen where something is already written or drawn only that portion should get overwritten which is to be occupied by the mouse cursor. Of the 64 bytes the first 32 bytes contain a bit mask which is first ANDed with the screen image, and then the second 32 bytes bit mask is XORed with the screen image.
The following program changes the mouse cursor in graphics mode to resemble an hour glass.
initmouse( ){i.x.ax = 0 ; int86 ( 0x33, &i, &o ) ;return ( o.x.ax == 0 ? -1 : 0 ) ;}showmouseptr( ){i.x.ax = 1 ; int86 ( 0x33, &i, &o ) ;}changecursor ( int *shape ){i.x.ax = 9 ; /* service number */i.x.bx = 0 ; /* actual cursor position from left */i.x.cx = 0 ; /* actual cursor position from top */i.x.dx = ( unsigned ) shape ; /* offset address of pointer image*/segread ( &s ) ;s.es = s.ds ; /* segment address of pointer */int86x ( 0x33, &i, &i, &s ) ;}
72.
Towers Of Hanoi
Suppose there are three pegs labeled A, B and C. Four disks are placed on peg A. The bottom-most disk is largest, and disks go on decreasing in size with the topmost disk being smallest. The objective of the game is to move the disks from peg A to peg C, using peg B as an auxiliary peg. The rules of the game are as follows:
Only one disk may be moved at a time, and it must be the top disk on one of the pegs. A larger disk should never be placed on the top of a smaller disk. Suppose we are to write a program to print out the sequence in which the disks should be moved such that all disks on peg A are finally transferred to peg C. Here it is...main( ){int n = 4 ;move ( n, 'A', 'B', 'C' ) ;}
move ( n, sp, ap, ep )int n ;char sp, ap, ep ;{if ( n == 1 )printf ( "\n Move from %c to %c ", sp, ep ) ;else{move ( n - 1, sp, ep, ap ) ;move ( 1, sp, ' ', ep ) ;move ( n - 1, ap, sp, ep ) ;}}
And here is the output...
Move from A to BMove from A to CMove from B to CMove from A to BMove from C to AMove from C to BMove from A to BMove from A to CMove from B to CMove from B to AMove from C to AMove from B to CMove from A to BMove from A to CMove from B to C
This problem is the famous Towers of Hanoi problem, wherein three pegs are to be employed for transferring the disks with the given criteria. Here's how we go about it. We have three pegs: the starting peg, sp, the auxiliary peg ap, and the ending peg, ep, where the disks must finally be. First, using the ending peg as an auxiliary or supporting peg, we transfer all but the last disk to ap. Next the last disk is moved from sp to ep. Now, using sp as the supporting peg, all the disks are moved from ap to ep. ‘A’, B and C denote the three pegs. The recursive function move( ) is called with different combinations of these pegs as starting, auxiliary and ending pegs.-------------------------------------------------------------------------------------------------
73.
What would be the output of following program?
struct syntax{int i ;float g ;char c ;}main( ){printf ( "I won't give you any error" ) ;}
Ans: The above program would get compiled successfully and on execution it would print the message given in printf(). What strikes in the above code snippet is the structure syntax which is declared but not terminated with the statement terminator, the semicolon. The compiler would not give any error message for it, as it assumes that main( ) function have a return type of struct syntax and hence would successfully compile and execute the program.-------------------------------------------------------------------------------------------------
The function biosmemory uses BIOS interrupt 0x12 to return the size of memory.-------------------------------------------------------------------------------------------------75.
Float FormatHow does C compiler stores float values ?
Ans: In C, the float values are stored in a mantissa and exponent form. While writing a number we specify the exponent part in the form of base 10. But, in case of C compiler, the exponent for floats is stored in the form of base 2. Obviously, because, computer stores the numbers in binary form. The C compiler follows an IEEE standard to store a float. The IEEE format expresses a floating-point number in a binary form known as `normalized' form. Normalization involves adjusting the exponent so that the "binary point" (the binary analog of the decimal point) in the mantissa always lies to the right of most significant nonzero digit. In binary representation, this means that the most significant digit of the mantissa is always a 1. This property of the normalized representation is exploited by the IEEE format when storing the mantissa. Let us consider an example of generating the normalized form of a floating point number. Suppose we want to represent the decimal number 5.375. Its binary equivalent can be obtained as shown below:2 | 5.375 x 2 = 0.750 0|------.750 x 2 = 1.500 12 | 2 1.500 x 2 = 1.000 1|------2 | 1 0|------| 0 1Writing remainders in reverse writing whole parts in the same order we get 101 order in which they are obtained we get 011 thus the binary equivalent of 5.375 would be 101.011. The normalized form of this binary number is
obtained by adjusting the exponent until the decimal point is to the right of most significant 1. In this case the result is 1.01011 x 22. The IEEE format for floating point storage uses a sign bit, a mantissa and an exponent for representing the power of 2. The sign bit denotes the sign of the number: a 0 represents a positive value and a 1 denotes a negative value. The mantissa is represented in binary. Converting the floating-point number to its normalized form results in a mantissa whose most significant digit is always 1. The IEEE format takes advantage of this by not storing this bit at all. The exponent is an integer stored in unsigned binary format after adding a positive integer bias. This ensures that the stored exponent is always positive. The value of the bias is 127 for floats and 1023 for doubles. Thus, 1.01011 x 22 is represented as shown below:--- --------------- ----------------------------------------------| 0 | 100 0000 1 | 010 1100 0000 0000 0000 0000 |--- ---------------- ---------------------------------------------sign bit exponent- mantissa stored in normalized form obtained after adding a bias127 to exponent 2
Data Structures
Which is the best sorting method?
Ans: There is no sorting method that is universally superior to all others. The programmer must carefully examine the problem and the desired results before deciding the particular sorting method. Some of the sorting methods are given below:Bubble sort : When a file containing records is to be sorted then Bubble sort is the best sorting method when sorting by address is used.
Bsort : It can be recommended if the input to the file is known to be nearly sorted.
Meansort : It can be recommended only for input known to be very nearly sorted.
Quick Sort : In the virtual memory environment, where pages of data are constantly being swapped back and forth between external and internal storage. In practical situations, quick sort is often the fastest available because of its low overhead and its average behavior.
Heap sort : Generally used for sorting of complete binary tree. Simple insertion sort and straight selection sort : Both are more efficient than bubble sort. Selection sort is recommended for small files when records are large and for reverse situation insertion sort is recommended. The heap sort and quick sort are both more efficient than insertion or selection for large number of data.
Shell sort : It is recommended for moderately sized files of several hundred elements.
Radix sort : It is reasonably efficient if the number of digits in the keys is not too large.
76.
Calculating Wasted Bytes On Disk
When a file gets stored on the disk, at a time DOS allocates one cluster for it. A cluster is nothing but a group of sectors. However, since all file sizes cannot be expected to be a multiple of 512 bytes, when a file gets stored often part of the cluster remains unoccupied. This space goes waste unless the file size grows to occupy these wasted bytes. Thefollowing program finds out how much space is wasted for all files in all the directories of the current drive.
#include <dir.h>#include <dos.h>#include <stdio.h>#include <string.h>#include <stdlib.h>unsigned bytes_per_cluster ;unsigned long wasted_bytes ;unsigned long num_files = 0 ;main( ){int ptr = 0, flag = 0, first = 0 ;struct ffblk f[50] ;struct dfree free ;/* get cluster information and calculate bytes per cluster */getdfree ( 0, &free ) ;bytes_per_cluster = free.df_bsec * free.df_sclus ;chdir ( "\\" ) ;/* check out files in root directory first */cal_waste( ) ;/* loop until all directories scanned */while ( ptr != -1 ){/* should I do a findfirst or a findnext? */if ( first == 0 )flag = findfirst ( "*.*", &f[ptr], FA_DIREC ) ;elseflag = findnext ( &f[ptr] ) ;while ( flag == 0 ){/* make sure its a directory and skip over . & .. entries */if ( f[ptr].ff_attrib == FA_DIREC && f[ptr].ff_name[0] != '.' ){flag = chdir ( f[ptr].ff_name ) ; /* try changing directories */if ( flag == 0 ) /* did change dir work? */{cal_waste( ) ;first = 0 ; /* set for findfirst on next pass */break ;}}flag = findnext ( &f[ptr] ) ; /* search for more dirs */
}if ( flag != 0 || ptr == 49 ) /* didn't find any more dirs */{ptr-- ;chdir ( ".." ) ; /* go back one level */first = 1 ; /* set to findnext on next pass */}elseptr++ ;}printf ( "There are %lu bytes wasted in %lu files.\n", wasted_bytes,num_files ) ;}cal_waste( ){int flag = 0 ;long full_cluster ;struct ffblk ff ;/* look for all file types */flag = findfirst ( "*.*", &ff, FA_RDONLY | FA_HIDDEN | FA_SYSTEM | FA_ARCH) ;while ( flag == 0 ){num_files++ ;full_cluster = ff.ff_fsize / bytes_per_cluster * bytes_per_cluster ;wasted_bytes += bytes_per_cluster - ( ff.ff_fsize - full_cluster ) ;flag = findnext ( &ff ) ;}}
Data Structures
Polish Notation
The method of writing all operators either before their operation, or after them, is called Polish notation, in honor of its discoverer, the Polish mathematician Jan Lukasiewicz. When the operators are written before their operands, it is called the prefix form. When the operators come after their operands. It is called the postfix form, or, sometimes reverse Polish form or suffix form. In this context, it is customary to use the coined phrase infix form to denote the usual custom of writing binary operators between their operands. For example, the expression A + B becomes +AB in prefix form and AB+ in postfix form. In the expression A + B x C, the multiplication is done first, so we convert it first, obtaining first A + ( BCx ) and then ABCx+ in postfix form. The prefix form of this expression is +A x BC. The prefix and postfix forms are not related by taking mirror images or other such simple transformation. Also all parentheses have been omitted in the Polish forms.
The C programming language does not let you nest functions. You cannot write a function definition inside another function definition, as in:
int fun1( ){int fun2() /* such nesting of functions is not allowed */{.....}}Because of this restriction it is not possible to hide function names inside a hierarchy. As a result all the functions that you declare within a program are visible to each other. This of course is not a major drawback since one can limit visibility by grouping functions within separate C source files that belong to different logical units of the program. C does, however, suffer in another way because of this design decision. It provides no easy way to transfer control out of a function except by returning to the expression that called the function. For the vast majority of function calls, that is a desirable limitation. You want the discipline of nested function calls and returns to help you understand flow of control through a program. Nevertheless, on some occasions that discipline is too restrictive. The program is sometimes easier to write, and to understand, if you can jump out of one or more function invocations at a single stroke. You want to bypass the normal function returns and transfer control to somewhere in an earlier function invocation.
For example, you may want to return to execute some code for error recovery no matter where an error is detected in your application. The setjmp and the longjmp functions provide the tools to accomplish this. The setjmp function saves the "state" or the "context" of the process and the longjmp uses the saved context to revert to a previous point in the program. What is the context of the process? In general, the context of a process refers to information that enables you to reconstruct exactly the way the process is at a particular point in its flow of execution. In C program the relevant information includes quantities such as values of SP, SS, FLAGS, CS, IP, BP, DI, ES, SI and DS registers.
To save this information Turbo C uses the following structure, which is defined, in the header file 'setjmp.h'.typedef struct{unsigned j_sp ;unsigned j_ss ;unsigned j_flag ;unsigned j_cs ;unsigned j_ip ;unsigned j_bp ;unsigned j_di ;unsigned j_es ;
unsigned j_si ;unsigned j_ds ;} jmp_buf[1] ;This is a system-dependent data type because different systems might require different amounts of information to capture the context of a process. In Turbo C, jmp_buf is simply an array of ten 2-byte integers. To understand the mechanics of setjmp and longjmp, look at the following codefragment.#include "setjmp.h"jmp_buf buf ;main( ){if ( setjmp ( buf ) == 0 )process( ) ;elsehandle_error( ) ; /* executed when longjmp is called */}process( ){int flag = 0 ;/* some processing is done here *//* if an error occurs during processing flag is set up */if ( flag )longjmp ( buf, 1 ) ;}
Upon entry to setjmp the stack contains the address of the buffer buf and the address of the if statement in the main function, to which setjmp will return. The setjmp function copies this return address as well as the current values of registers, SP, SS, FLAGS, BP, DI, ES, SI and DS, into the buffer buf. Then setjmp returns with a zero. In this case, the if statement is satisfied and the process( ) function is called. If something goes wrong in process( ) (indicated by the flag variable), we call longjmp with two arguments: the first is the buffer that contains the context to which we will return. When the stack reverts back to this saved state, and the return statement in longjmp is executed, it will be as if we were returning from the call to setjmp, which originally saved the buffer buf. The second argument to longjmp specifies the return value to be used during this return. It should be other than zero so that in the if statement we can tell whether the return is induced by a longjmp.
The setjmp/longjmp combination enables you to jump unconditionally from one C function to another without using the conventional return statements. Essentially, setjmp marks the destination of the jump and longjmp is a non-local goto that executes the jump.Data Structures
Comparison Trees...
The comparison trees also called decision tree or search tree of an algorithm, is obtained by tracing through the actions of the algorithm, representing each comparison of keys by a vertex of the tree (which we draw as a circle). Inside the
circle we put the index of the key against which we are comparing the target key. Branches (lines) drawn down from the circle represent the possible outcomes of the comparison and are labeled accordingly. When the algorithm terminates, we put either F (for failure) or the location where the target is found at the end of the appropriate branch, which we call a leaf, and draw as a square. Leaves are also sometimes called end vertices or external vertices of the tree. The remaining vertices are called the internal vertices of the tree. The comparison tree for sequential search is especially simple.-------------------------------------------------------------------------------------------------78.
Suppose we have a floating-point number with higher precision say 12.126487687 and we wish it to be printed with only precision up to two decimal places. How can I do this?
Ans. This can achieved through the use of suppression char '*' in the format string of printf( ) which is shown in the following program.main( ){int p = 2 ;float n = 12.126487687 ;printf ( "%.*f",p, n ) ;}-------------------------------------------------------------------------------------------------79.Spawning
All programs that we execute from DOS prompt can be thought of as children of COMMAND.COM. Thus, the program that we execute is a child process, whereas COMMAND.COM running in memory is its parent. The process of a parent process giving birth to a child process is known as 'spawning'. If the spawned program so desires, it may in turn spawn children of its own, which then execute and return control to their parent. Who is the parent of COMMAND.COM? COMMAND.COM itself. We can trace the ancestors of our program using the field Parent Process ID (PID) present at offset 0x16 in the Program Segment Prefix (PSP). To trace this ancestry our program should first locate its PSP, extract the parent process ID from it and then use this to find PSP of the parent. This process can be repeated till we reach COMMAND.COM (process ID of COMMAND.COM is its own PSP), the father of all processes. Here is a program which achieves this...
/* SPAWN.C */#include "dos.h"
unsigned oldpsp, newpsp, far *eb_seg, i ;char far *eb_ptr ;
main( )
{oldpsp = _psp ;
while ( 1 ){printf ( "\n" ) ;printname ( oldpsp ) ;printf ( " spawned by " ) ;
On running the program from within TC the output obtained is shown below. SPWAN.EXE (58A9) spawned by TC.EXE (0672) TC.EXE (0672) spawned by COMMAND.COM (05B8). The program simply copies its own process ID in the variable oldpsp and then uses it to extract its own filename from its environment block. This is done by the function printname( ). The value in oldpsp is then used to retrieve the parent's PID in newpsp. From there the program loops reporting the values of oldpsp, newpsp and the
corresponding file names until the program reaches COMMAND.COM.
The printname( ) function first locates the environment block of the program and then extracts the file name from the environment block. The fnsplit( ) function has been used to eliminate the path present prior to the file name. Do not run the program from command line since it would give you only one level of ancestry.
Data Structures
Choosing the data structures to be used for information retrieval. For problems of information retrieval, consider the size, number, and location of the records along with the type and structure of the keys while choosing the data structures to be used. For small records, high-speed internal memory will be used, and binary search trees will likely prove adequate. For information retrieval from disk files, methods employing multiway branching, such as trees, B-trees , and hash tables, will usually be superior. Tries are particularly suited to applications where the keys are structured as a sequence of symbols and where the set of keys is relatively dense in the set of all possible keys. For other applications, methods that treat the key as a single unit will often prove superior. B-trees, together with various generalization and extensions, can be usefully applied to many problems concerned with external information retrieval.
80.
Variably Dimensioned Arrays
While dealing with Scientific or Engineering problems one is often required to make use of multi-dimensioned array. However, when it comes to passing multidimensional arrays to a function C is found wanting. This is because the C compiler wants to know the size of all but the first dimension of any array passed to a function. For instance, we can define a function compute ( int n, float x[] ), but not compute ( int n, x[][]).
Thus, C can deal with variably dimensioned 1-D arrays, but when an array has more than one dimension, the C compiler has to know the size of the last dimensions expressed as a constant. This problem has long been recognized, and some of the solutions that are often used are:
Declare the arrays in the functions to be big enough to tackle all possible situations. This can lead to a wastage of lot of precious memory in most cases. Another solution is to construct multiple-dimension array as an array of pointers. For example, a matrix (2-D array) of floats can be declared as a 1-D array of float pointers, with each element pointing to an array of floats. The problem with this method is that the calling function has to define all arrays in this fashion.
This means that any other computations done on the arrays must take this special structure into account.
Another easy solution, though seldom used, exists. This is based on the following method:
Pass the array to the function as though it is a pointer to an array of floats (or the appropriate data type), no matter how many dimensions the array actually has, along with the dimensions of the array. Reference individual array elements as offsets from this pointer.Write your algorithm so that array elements are accessed in storage order. The following program for multiplying two matrices illustrates thisprocedure.# define M 3# define N 2# define P 4
main( ){int i, j ;for ( i = 0 ; i < M ; i++ )for ( j = 0 ; j < N ; j++ )a[i][j] = i + j ;
for ( i = 0 ; i < N ; i++ )for ( j = 0 ; j < P ; j++ )b[i][j] = i + j ;
mulmat ( M, N, P, a, b, c ) ;for ( i = 0 ; i < M ; i++ ){printf ( "\n" ) ;for ( j = 0 ; j < P ; j++ )printf ( "%f\t", c[i][j] ) ;}}
void mulmat ( int m, int n, int p, float *a, float *b, float *c ){float *ptrtob, *ptrtoc ;int i, j, k, nc ;
/* set all elements of matrix c to 0 */for ( i = 0 ; i < m * p ; i++ )*( c + i ) = 0 ;
for ( i = 0 ; i < m ; i++ ){ptrtob = b ;for ( k = 0 ; k < n ; k++ ){ptrtoc = c ;
for ( j = 0 ; j < p ; j++ )*ptrtoc++ += *a * *ptrtob++ ;a++ ;}c += p ;}}
We know that C stores array elements in a row-major order. Hence to ensure that the elements are accessed in the storage order the above program uses a variation of the normal matrix-multiplication procedure. The pseudo code for this is given below:for i = 1 to mfor j = 1 to pc[i][j] = 0endfor k = 1 to nfor j = 1 to pc[i][j] = c[i][j] + a[i][k] * b[k][j]endendend-------------------------------------------------------------------------------------------------81.
Why is it not possible to scan strings from keyboard in case of array of pointers to string?
Ans: When an array is declared, dimension of array should be specified so that compiler can allocate memory for the array. When array of pointers to strings is declared its elements would contain garbage addresses. These addresses would be passed to scanf( ). So strings can be received but they would get stored at unkown locations. This is unsafe.-------------------------------------------------------------------------------------------------82.Bit Arrays
If in a program a variable is to take only two values 1 and 0, we really need only a single bit to store it. Similarly, if a variable is to take values from 0 to 3, then two bits are sufficient to store these values. And if a variable is to take values from 0 through 7, then three bits will be enough, and so on. Why waste an entire integer when one or two or three bits will do? Because there aren't any one bit or two bit or three bit data types available in C. However, when there are several variables whose maximum values are small enough to pack into a single memory location, we can use `bit fields' to store several values in a single integer. Bit fields are discussed in most standard C texts. They are usually used when we want to store assorted information which can be accommodated in 1, 2, 3 bits etc.
For example, the following data about an employee can be easily stored using bit fields.
male or femalesingle, married, divorced or widowedhave one of the eight different hobbiescan choose from any of the fifteen different schemes proposed by the company to pursue his/her hobby.
This means we need one bit to store gender, two to store marital status, three for hobby, and four for scheme (with one value used for those who are not desirous of availing any of the schemes). We need ten bits altogether, which means we can pack all this information into a single integer, since an integer is 16 bits long.
At times we may need to store several True or False statuses. In such cases instead of using bit fields using an array of bits would be more sensible. On this array we may be required to perform the following operations:
Set a bit (make it 1).Clear a bit (make it 0).Test the status of a bit in the array.Reach the appropriate bit slot in the array.Generate a bit mask for setting and clearing a bit.We can implement these operations using macros given below:
#define CHARSIZE 8#define MASK ( y ) ( 1 << y % CHARSIZE )#define BITSLOT ( y ) ( y / CHARSIZE )#define SET ( x, y ) ( x[BITSLOT( y )] |= MASK( y ) )#define CLEAR ( x, y ) ( x[BITSLOT( y )] &= ~MASK( y ) )#define TEST ( x, y ) ( x[BITSLOT( y )] & MASK( y ) )#define NUMSLOTS ( n ) ( ( n + CHARSIZE - 1) / CHARSIZE )
Using these macros we can declare an array of 50 bits be saying,
char arr[NUMSLOTS(50)] ;To set the 20th bit we can say,
SET(arr, 20 ) ;And if we are to test the status of 40th bit we may say,if ( TEST ( arr, 40 ) )Using bit arrays often results into saving a lot of precious memory. For example, the following program which implements the Sieve of Eratosthenes for generating prime numbers smaller than 100 requires only 13 bytes. Had we implemented the same logic using an array of integers we would have required an array of 100 integers, that is 200 bytes.#include <stdio.h>#include <string.h>
#define MAX 100
main( ){char arr[NUMSLOTS( MAX )] ;int i, j ;
memset ( arr, 0, NUMSLOTS( MAX ) ) ;for ( i = 2 ; i < MAX ; i++ ){if ( !TEST ( arr, i ) ){printf ( "\n%d", i ) ;for ( j = i + i ; j < MAX ; j += i )SET ( arr, j ) ;}}}-------------------------------------------------------------------------------------------------83.Information Hiding in C
Though C language doesn't fully support encapsulation as C++ does, there is a simple technique through which we can implement encapsulation in C. The technique that achieves this is modular programming in C. Modular programming requires a little extra work from the programmer, but pays for itself during maintenance. To understand this technique let us take the example of the popular stack data structure. There are many methods of implementing a stack (array, linked list, etc.). Information hiding teaches that users should be able to push and pop the stack's elements without knowing about the stack's implementation. A benefit of this sort of information hiding is that users don't have to change their code even if the implementation details change.
Consider the following scenario:
To be able to appreciate the benefits of modular programming and thereby information hiding, would first show a traditional implementation of the stack data structure using pointers and a linked list of structures. The main( ) function calls the push( ) and pop( ) functions.
#include <alloc.h>typedef int element ;void initialize_stack ( struct node ** ) ;void push ( struct node **, element ) ;element pop ( struct node * ) ;int isempty ( struct node * ) ;struct node{element data ;struct node *next ;} ;void main( ){struct node *top ;element num ;
initialize_stack ( &top ) ;push ( &top, 10 ) ;push ( &top, 20 ) ;push ( &top, 30 ) ;if ( isempty ( top ) )printf ( "\nStack is empty" ) ;else{num = pop ( top ) ;printf ( "\n Popped %d", num ) ;}}void initialize_stack ( struct node **p ){*p = NULL ;}void push ( struct node **p, element n ){struct node *r ;r = ( struct node *) malloc ( sizeof ( struct node ) ) ;r -> data = n ;if ( *p == NULL )r -> next = NULL ;elser -> next = *p ;*p = r ;}element pop ( struct node *p ){element n ;struct node *r ;n = p -> data ;r = p ;p = p -> next ;free ( r ) ;return ( n ) ;}int isempty ( struct node *p ){if ( p == NULL )return ( -1 ) ;elsereturn ( 0 ) ;}Notice how the specific implementation of the data structure is strewn throughout main( ). main( ) must see the definition of the structure node to use the push( ), pop( ), and other stack functions. Thus the implementation is not hidden, but is mixed with the abstract operations.
Data Structures
Radix Sort
This sorting technique is based on the values of the actual digits in the positional representations of the numbers being sorted. Using the decimal base, for example, where the radix is 10, the numbers can be partitioned into ten groups on the
sorter. For example, to sort a collection of numbers where each number is a four-digit number, then, All the numbers are first sorted according to the the digit at unit's place.In the second pass, the numbers are sorted according to the digit at tenth place. In the third pass, the numbers are sorted according to the digit at hundredth place. In the forth and last pass, the numbers are sorted according to the digit at thousandth place.During each pass, each number is taken in the order in which it appears in partitions from unit's place onwards. When these actions have been performed for each digit, starting with the least significant and ending with most significant, the numbers are sorted. This sorting method is called the radix sort.
Let us take another example. Suppose we have a list of names. To sort these names using radix sort method we will have to classify them into 26 groups The list is first sorted on the first letter of each name, i.e. the names are arranged in 26 classes, where the first class consists of those names that begin with alphabet 'A', the second class consists of those names that begin with alphabet 'B' and so on. During the second pass each class is alphabetized according to the second letter of the name, and so on. 84.
Exception Handling in C
Consider the following program:
#include <math.h>void main( ){float i ;i = pow ( -2, 3 ) ;printf ( "%f", i ) ;}
int matherr ( struct exception *a ){if ( a -> type == DOMAIN ){if ( !strcmp ( a -> name, "pow" ) ){a -> retval = pow ( - ( a -> arg1 ), a -> arg2 ) ;return 1 ;}}return 0 ;}
If we pass a negative value in pow( ) function a run time error occurs. If we wish to get the proper output even after passing a negative value in the pow( ) function we must handle the run time error. For this, we can define a function matherr( ) which is declared in the 'math.h' file. In this function we can detect the run-time error and write our code to correct the error. The elements of the exception structure
receives the function name and arguments of the function causing the exception.
Data Structures
AVL Trees
For ideal searching in a binary search tree, the heights of the left and right sub-trees of any node should be equal. But, due to random insertions and deletions performed on a binary search tree, it often turns out to be far from ideal. A close approximation to an ideal binary search tree is achievable if it can be ensured that the difference between the heights of the left and the right sub trees of any node in the tree is at most one. A binary search tree in which the difference of heights of the right and left sub-trees of any node is less than or equal to one is known as an AVL tree. AVL tree is also called as Balanced Tree. The name "AVL Tree" is derived from the names of its inventors who are Adelson-Veilskii and Landi. A node in an AVL tree have a new field to store the "balance factor" of a node which denotes the difference of height between the left and the right sub-trees of the tree rooted at that node. And it can assume one of thethree possible values {-1,0,1}.-------------------------------------------------------------------------------------------------85.
Unique combinations for a given number
How do I write a program which can generate all possible combinations of numbers from 1 to one less than the given number ?main( ){long steps, fval, bstp, cnt1 ;int num, unit, box[2][13], cnt2, cnt3, cnt4 ;printf ( "Enter Number " ) ;scanf ( "%d", &num ) ;num = num < 1 ? 1 : num > 12 ? 12 : num ;for ( steps = 1, cnt1 = 2 ; cnt1 <= num ; steps *= cnt1++ ) ;for ( cnt1 = 1 ; cnt1 <= steps ; cnt1++ ){for ( cnt2 = 1 ; cnt2 <= num ; cnt2++ )box[0][cnt2] = cnt2 ;for ( fval = steps, bstp = cnt1, cnt2 = 1 ; cnt2 <= num ; cnt2++ ){if ( bstp == 0 ){cnt4=num ;while ( box[0][cnt4] == 0 )cnt4-- ;}else{fval /= num - cnt2 + 1 ;unit = ( bstp + fval - 1 ) / fval ;
bstp %= fval ;for ( cnt4 = 0, cnt3 = 1 ; cnt3 <= unit ; cnt3++ )while ( box[0][++cnt4] == 0 ) ;}box[1][cnt2] = box[0][cnt4] ;box[0][cnt4] = 0 ;}printf ( "\nSeq.No.%ld:", cnt1 ) ;for ( cnt2 = 1 ; cnt2 <= num ; cnt2++ )printf ( " %d", box[1][cnt2] ) ;}}This program computes the total number of steps. But instead of entering into the loop of the first and last combination to be generated it uses a loop of 1 to number of combinations. For example, in case of input being 5 the number of possible combinations would be factorial 5, i.e. 120. The program suffers from the limitation that it cannot generate combinations for input beyond 12 since a long int cannot handle the resulting combinations.
Data Structures
Hashing...
Hashing or hash addressing is a searching technique. Usually, search of an element is carried out via a sequence of comparisons. Hashing differs from this as it is independent of the number of elements n in the collection of data. Here, the address or location of an element is obtained by computing some arithmetic function. Hashing is usually used in file management. The general idea is of using the key to determine the address of a record. For this, a function fun( ) is applied to each key, called the hash function. Some of the popular hash functions are: 'Division' method, 'Midsquare' method, and 'Folding' method. Two records cannot occupy the same position. Such a situation is called a hash collision or a hash clash. There are two basic methods of dealing with a hash clash. The first technique, called rehashing, involves using secondary hash function on the hash key of the item. The rehash function is applied successively until an empty position is found where the item can be inserted. If the hash position of the item is found to be occupied during a search, the rehash function is again used to locate the item. The second technique, called chaining, builds a linked list of all items whose keys hash to the same values. During search, this short linked list is traversed sequentially for the desired key. This technique involves adding an extra link field to each table position.-------------------------------------------------------------------------------------------------
86.
The following program demonstrates how to get input from the user in graphics mode, echoed in the current colors and font size and font style.
#define ON 1#define OFF 0#include <graphics.h>main( ){char nameString[80], ageString[80] ;int age, gd = DETECT, gm ;initgraph ( &gd, &gm, "c:\\tc\\bgi" ) ;setbkcolor ( BLUE ) ;setcolor ( YELLOW ) ;settextstyle ( GOTHIC_FONT, HORIZ_DIR, 0 ) ;moveto ( 0, 0 ) ;outtext ( "Enter your name: " ) ;getGrString ( nameString ) ;moveto ( 0, gety( ) + textheight ( "A" ) ) ;outtext ( "Name: " ) ;outtext ( nameString ) ;moveto ( 0, gety( ) + textheight ( "A" ) ) ;outtext ( "Press key to exit! " ) ;getch( ) ;closegraph( ) ;restorecrtmode( ) ;}getGrString ( char *inputString ){int stringIndex = 0, oldColor ;char ch, outString[2] ;/* xVal will store the screen position for each char */int xVal[255] ;outString[1] = 0 ;xVal[0] = getx( ) ;do{cursor ( ON ) ;ch = getch( ) ;cursor ( OFF ) ;if ( ch == 0 ) /* avoid dealing with all special keys */getch( ) ;else{if ( ch == 8 ) /* backspace */{oldColor = getcolor( ) ;--stringIndex ;if ( stringIndex < 0 )stringIndex = 0 ;/* move to ( old horz position, current vert position ) */moveto ( xVal[stringIndex], gety( ) ) ;setcolor ( getbkcolor( ) ) ;outString[0] = inputString[stringIndex] ;outtext ( outString ) ;moveto ( xVal [stringIndex], gety( ) ) ;setcolor ( oldColor ) ;}else{inputString[stringIndex] = ch ;outString[0] = ch ;
outtext ( outString ) ;++stringIndex ;xVal[stringIndex] = getx( ) ;}}} while ( ch != 13 && ch != 10 ) ;inputString[stringIndex] = 0 ;}cursor ( int on ){int curX, oldColor ;/* we'll use an underscore as a cursor */char uBarStr[2] = { '_', 0 } ;if ( !on ){oldColor = getcolor( ) ;setcolor ( getbkcolor( ) ) ;}/* save horizontal position before drawing cursor */curX = getx( ) ;outtext ( uBarStr ) ;moveto ( curX, gety( ) ) ;/* if we changed the color to erase cursor, change it back */if ( !on )setcolor ( oldColor ) ;}The function getGrString( ) echoes graphically the user input and stores it in a buffer, and the function cursor( ) handles the cursor position.
System Utility
What is garbage collection?
Ans: Suppose some memory space becomes reusable because a node is released from a linked list. Hence, we want the space to be available for future use. One way to bring this about is to immediately reinsert the space into the free-storage list. However, this method may be too time-consuming for the operating system. The operating system may periodically collect all the deleted space onto the free-storage list. The technique that does this collection is called Garbage Collection. Garbage Collection usually takes place in two steps: First the Garbage Collector runs through all lists, tagging whose cells are currently in use, and then it runs through the memory, collecting all untagged space onto the free-storage list. The Garbage Collection may take place when there is only some minimum amount of space or no space at all left in the free-storage list, or when the CPU is idle and has time to do the collection. Generally speaking, the Garbage Collection is invisible to the programmer.
87.
How do I get the time elapsed between two function calls ?
Ans: The function difftime( ) finds the difference between two times. It calculates the elapsed time in seconds and returns the difference between two times as a double value.
main( ){int a[] = { 2, -34, 56, 78, 112, 33, -7, 11, 45, 29, 6 } ;int s ;time_t t1, t2 ; // time_t defines the value used for time function
s = sizeof ( a ) / 2 ;t1 = time ( NULL ) ;sel_sort ( a, s ) ; // sort array by selection sortbub_sort ( a, s ) ; // sort array by bubble sort methodt2 = time ( NULL ) ;printf ( "\nThe difference between two function calls is %f", difftime (t2, t1 ) ) ;}
In the above program we have called difftime( ) function that returns the time elapsed from t1 to t2.-------------------------------------------------------------------------------------------------88.
Generalmain( ){char *s ;s = fun ( 128, 2 ) ;printf ( "\n%s", s ) ;}fun ( unsigned int num, int base ){static char buff[33] ;char *ptr ;ptr = &buff [ sizeof ( buff ) - 1 ] ;*ptr = '\0' ;do{*--ptr = "0123456789abcdef"[ num % base ] ;num /= base ;} while ( num != 0 ) ;return ptr ;}The above program would convert the number 128 to the base 2. You can convert a number to a hexadecimal or octal form by passing the number and the base, to the function fun( ).
Data Structures
What is a priority queue?
Ans: As we know in a stack, the latest element is deleted and in a queue the oldest element is deleted. It may be required to delete an element with the highest priority in the given set of values and not only the oldest or the newest one. A data structure that supports efficient insertions of a new element and deletions of elements with the highest priority is known as priority queue. There are two types of priority queues: an ascending priority queue is a collection of items into which items can be inserted arbitrarily and from which only the smallest item can be removed. A descending order priority queue is similar but allows only the largest item to be deleted.-------------------------------------------------------------------------------------------------89.
What is the difference between const char *p, char const *p, and char* const p ?
'const char *p' and 'char const *p' are the same, i.e. p points to a constant character. On the other hand, 'char* const p' means p is a constant pointer pointing to a character which means we cannot change the pointer p but we can change the character which p is pointing to.-------------------------------------------------------------------------------------------------90.
What's the difference between a null pointer, a NULL macro, the ASCII NUL character and a null string?
Ans: A null pointer is a pointer which doesn't point anywhere. A NULL macro is used to represent the null pointer in source code. It has a value 0 associated with it. The ASCII NUL character has all its bits as 0 but doesn't have any relationship with the null pointer. The null string is just another name for an empty string "".
System Utility
Sparse Matrix...
A sparse matrix is one where most of its elements are zero. There is no precise definition as to know whether a matrix is sparsed or not, but it is a concept which we all can recognize intuitively. The natural method of representing matrices in memory as two-dimensional arrays may not be suitable for sparse matrices. That is one may save space by storing only those entries which may be nonzero. If this is done, then the matrix may be thought of as an ordered list of non-zero elements only. Information about a non-zero element has three parts:an integer representing its row,an integer representing its column andthe data associated with this element.
That is, each element of a matrix is uniquely characterized by its row and column position, say i, j. We might store that matrix as a list of 3-tuples of the form (i, j, data), as shown below,
Although the non-zero elements may be stored in the array in any order, keeping them ordered in some fashion may be advantageous for further processing. Note that above array is arranged in increasing order of the row number of non-zero elements. Moreover, for elements in the same row number, the array is arranged in order of increasing column number.-------------------------------------------------------------------------------------------------91.
Pointers
What does the error "Null Pointer Assignment" mean and what causes this error?
Ans: The Null Pointer Assignment error is generated only in small and medium memory models. This error occurs in programs which attempt to change the bottom of the data segment. In Borland's C or C++ compilers, Borland places four zero bytes at the bottom of the data segment, followed by the Borland copyright notice "Borland C++ - Copyright 1991 Borland Intl.". In the small and medium memory models, a null pointer points to DS:0000. Thus assigning a value to the memory referenced by this pointer will overwrite the first zero byte in the data segment. At program termination, the four zeros and the copyright banner are checked. If either has been modified, then the Null Pointer Assignment error is generated. Note that the pointer may not truly be null, but may be a wild pointer that references these key areas in the data segment.
Data Structures
How to build an expression trees ?
Ans: An expression tree is a binary tree which is built from simple operands and operators of an (arithmetic or logical ) expression by placing simple operands as the leaves of a binary tree and the operators as the interior nodes. If an operator is binary , then it has two nonempty subtrees, that are its left and right operands (either simple operands or sub expressions). If an operator is unary, then only one of its subtrees is nonempty, the one on the left or right according as the operator is written on the right or left of its operand. We traditionally write some unary operators to the left of their operands, such as "-" ( unary negation) or the standard functions like log( ), sin( ) etc. Others are written on the right, such as the factorial function ()!. If the operator is written on the left, then in the expression tree we take its left subtree as empty. If it appears on the right, then its right subtree will be empty. An example of an expression tree is shown below for the expression ( -a < b ) or ( c + d ) .
Can we get the remainder of a floating point division ?
Ans : Yes. Although the % operator fails to work on float numbers we can still get the remainder of floating point division by using a function fmod( ). The fmod( ) function divides the two float numbers passed to it as parameters and returns the remainder as a floating-point value. Following program shows fmod( ) function at work.
#include <math.h>
main( ){printf ( "%f", fmod ( 5.15, 3.0 ) ) ;}
The above code snippet would give the output as 2.150000.-------------------------------------------------------------------------------------------------93.
How to extract the integer part and a fractional part of a floating point number?
Ans: C function modf( ) can be used to get the integer and fractional part of a floating point.
#include "math.h"
main( ){double val, i, f ;val = 5.15 ;f = modf ( val, &i ) ;printf ( "\nFor the value %f integer part = %f and fractional part = %f",val, i, f ) ;}
The output of the above program will be:
For the value 5.150000 integer part = 5.000000 and fractional part =0.150000
94.
How do I define a pointer to a function which returns a char pointer?Ans:char * ( *p )( ) ;ortypedef char * ( * ptrtofun )( ) ;ptrtofun p ;
Here is a sample program which uses this definition.main( ){typedef char * ( * ptrtofun ) ( ) ;char * fun( ) ;ptrtofun fptr ;char *cptr ;fptr = fun ;cptr = (*fptr) ( ) ;printf ( "\nReturned string is \"%s\"", cptr ) ;}char * fun( ){static char s[ ] = "Hello!" ;printf ( "\n%s", s ) ;return s ;}-------------------------------------------------------------------------------------------------95.What's wrong with the following declaration: char* ptr1, ptr2 ; get errors when I try to use ptr2 as a pointer.
Ans: char * applies only to ptr1 and not to ptr2. Hence ptr1 is getting declared as a char pointer, whereas, ptr2 is being declared merely as a char. This can be rectified in two ways :char *ptr1, *ptr2 ;typedef char* CHARPTR ; CHARPTR ptr1, ptr2 ;-------------------------------------------------------------------------------------------------96.
How to use scanf( ) to read the date in the form of dd-mm-yy?
Ans: To read the date in the form of dd-mm-yy one possible way is,int dd, mm, yy ;char ch ; /* for char '-' */printf ( "\nEnter the date in the form of dd-mm-yy : " ) ;scanf( "%d%c%d%c%d", &dd, &ch, &mm, &ch, &yy ) ;Another way is to use suppression character * is as follows:int dd, mm, yy ;scanf( "%d%*c%d%*c%d", &dd, &mm, &yy ) ;The suppression character '*' suppresses the input read from the standard input buffer for the assigned control character.-------------------------------------------------------------------------------------------------97.
Why the output of sizeof ( 'a' ) is 2 and not 1 ?Ans: Character constants in C are of type int, hence sizeof ( 'a' ) is equivalent to sizeof ( int ), i.e. 2. Hence the output comes out to be 2 bytes.-------------------------------------------------------------------------------------------------
98.
Can we use scanf( ) function to scan a multiple words string through keyboard?
Ans: Yes. Although we usually use scanf( ) function to receive a single word string and gets( ) to receive a multi-word string from keyboard we can also use scanf( ) function for scanning a multi-word string from keyboard. Following program shows how to achieve this.
In the scanf( ) function we can specify the delimiter in brackets after the ^ character. We have specified '\n' as the delimiter. Hence scanf( ) terminates only when the user hits Enter key.-------------------------------------------------------------------------------------------------99.How to set the system date through a C program ?
Ans: We can set the system date using the setdate( ) function as shown in the following program. The function assigns the current time to astructure date.
How can I write a general-purpose swap without using templates?
Ans: Given below is the program which uses the stringizing preprocessor directive ## for building a general purpose swap macro which can swap two integers, two floats, two chars, etc.#define swap( a, b, t ) ( g ## t = ( a ), ( a ) = ( b ), ( b ) = g ## t )
int gint;char gchar;float gfloat ;main( ){int a = 10, b = 20 ;char ch1 = 'a' , ch2 = 'b' ;float f1 = 1.12, f2 = 3.14 ;swap ( a, b, int ) ;printf ( "\na = %d b = %d", a, b ) ;swap ( ch1, ch2, char ) ;printf ( "\nch1 = %c ch2 = %c", ch1, ch2 ) ;swap ( f1, f2, float ) ;printf ( "\nf1 = %4.2f f2 = %4.2f", f1, f2 ) ;}swap ( a, b, int ) would expand to,( gint = ( a ), ( a ) = ( b ), ( b ) = gint )-------------------------------------------------------------------------------------------------101.What is a heap ?
Ans : Heap is a chunk of memory. When in a program memory is allocated dynamically, the C run-time library gets the memory from a collection of unused memory called the heap. The heap resides in a program's data segment. Therefore, the amount of heap space available to the program is fixed, and can vary from one program to another.
102.
How to obtain a path of the given file?
Ans: The function searchpath( ) searches for the specified file in the subdirectories of the current path. Following program shows how to make use of the searchpath( ) function.
Can we get the process identification number of the current program?
Ans: Yes! The macro getpid( ) gives us the process identification number of the program currently running. The
process id. uniquely identifies a program. Under DOS, the getpid( ) returns the Program Segment Prefix as the process id. Following program illustrates the use of this macro.#include <stdio.h>#include <process.h>
void main( ){printf ( "The process identification number of this program is %X\n",getpid( ) ) ;}
Here, the function vfpf( ) has called vfprintf( ) that take variable argument lists. va_list is an array that holds information required for the macros va_start and va_end. The macros va_start and va_end provide a portable way to access the variable argument lists. va_start would set up a pointer argptr to point to the first of the variable arguments being passed to the function. The macro va_end helps the called function to perform a normal return.-------------------------------------------------------------------------------------------------105.Can we change the system date to some other date?
Ans: Yes, We can! The function stime( ) sets the system date to the specified date. It also sets the system time. The time and date is measured in seconds from the 00:00:00 GMT, January 1, 1970. The following program shows how to use this function.#include <stdio.h>#include <time.h>
void main( ){time_t tm ;int d ;
tm = time ( NULL ) ;
printf ( "The System Date : %s", ctime ( &tm ) ) ;printf ( "\nHow many days ahead you want to set the date : " ) ;scanf ( "%d", &d ) ;
tm += ( 24L * d ) * 60L * 60L ;
stime ( &tm ) ;printf ( "\nNow the new date is : %s", ctime ( &tm ) ) ;}In this program we have used function ctime( ) in addition to function stime( ). The ctime( ) function converts time value to a 26-character long string that contains date and time.-------------------------------------------------------------------------------------------------106.
How to use function strdup( ) in a program?
Ans : The string function strdup( ) copies the given string to a new location. The function uses malloc( ) function to allocate space required for the duplicated string. It takes one argument a pointer to the string to be duplicated. The total number of characters present in the given string plus one bytes get allocated for the new string. As this function uses malloc( ) to allocate memory, it is the programmer’s responsibility to deallocate the memory using free( ).#include <stdio.h>#include <string.h>#include <alloc.h>
On including a file twice I get errors reporting redefinition of function.How can I avoid duplicate inclusion?
Ans: Redefinition errors can be avoided by using the following macro definition. Include this definition in the header file.#if !defined filename_h#define filename_h/* function definitions */#endifReplace filename_h with the actual header file name. For example, if name of file to be included is 'goto.h' then replace filename_h with 'goto_h'.-------------------------------------------------------------------------------------------------108.How to write a swap( ) function which swaps the values of the variables using bitwise operators.
Ans: Here is the swap( ) function.swap ( int *x, int *y ){*x ^= *y ;*y ^= *x ;*x ^= *y ;}The swap( ) function uses the bitwise XOR operator and does not require any temporary variable for swapping.
NETWORKS############################1. What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
2. What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
3. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
4. What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
5. What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
6. What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
7. What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
8.What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
9. What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
10. What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
11. What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
12. What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
13. What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
14. What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
15. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
16. What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
17. How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
18. What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
19. What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
20. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N
where N is no-of-bits represented by each signal shift.
21. What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
22. What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
23. Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
24. What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN protocols.
It consists of the following:
* 802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols. * 802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs. * Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5). * 802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.25. What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
26. What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
27. What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
28. What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
29. What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
30. What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
31. What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
32. What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
33. What are major types of networks and explain?
* Server-based network * Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
34. What are the important topologies for networks?
* BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
35. What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
36. What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
37. Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
38. What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
39. What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
40. Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
41. What is logical link control?
One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.
42. What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
43. What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
44. What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
45. What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
46. What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
47. What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all
the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
48. What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
49. What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
50. Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
51. What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol. 52. What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.
53. What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
54. What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
55. What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
56. What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
57. What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
58. What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session. 59. What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
60. What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
61. What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
62. What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
63. What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
64. What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
65. What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@C++@@@@@@@@@@@@@@@@@@@@@@@C++====>1.
Can we declare a static function as virtual?
Ans: No. The virtual function mechanism is used on the specific object that determines which virtual function to call.
Since the static functions are not any way related to objects, they cannot be declared as virtual.-------------------------------------------------------------------------------------------------2.
Can user-defined object be declared as static data member of another class?
Ans: Yes. The following code shows how to initialize a user-defined object.
#include
class test { int i ; public : test ( int ii = 0 ) { i = ii ; } } ;
class sample { static test s ; } ; test sample::s ( 26 ) ;
Here we have initialized the object s by calling the one-argument constructor. We can use the same convention to initialize the object by calling multiple-argument constructor.
What is forward referencing and when should it be used?
Ans: Consider the following program: class test { public : friend void fun ( sample, test ) ; } ;
class sample { public : friend void fun ( sample, test ) ; } ;
void fun ( sample s, test t ) { // code }
void main( ) { sample s ; test t ; fun ( s, t ) ; }This program would not compile. It gives an error that sample is undeclared identifier in the statement friend void fun ( sample, test ) ; of the class test. This is so because the class sample is defined below the class test and we are using it before its definition. To overcome this error we need to give forward reference of the class sample before the definition of class test. The following statement is the forward reference of class sample. Forward referencing is generally required when we make a class or a function as a friend.-------------------------------------------------------------------------------------------------4.
The istream_withassign class has been derived from the istream class and overloaded assignment operator has been added to it. The _withassign classes are much like their base classes except that they include overloaded assignment operators. Using these operators the objects of the _withassign classes can be copied. The istream, ostream, and iostream classes are made uncopyable by making their overloaded copy constructor and assignment operators private.-------------------------------------------------------------------------------------------------5.
How do I write my own zero-argument manipulator that should work same as hex?
We all know that a const variable needs to be initialized at the time of declaration. Then how come the program given below runs properly even when we have not initialized p?
#include void main( ) { const char *p ; p = "A const pointer" ; cout << p ; } Ans: The output of the above program is 'A const pointer'. This is because in this program p is declared as 'const char*' which means that value stored at p will be constant and not p and so the program works properly
How do I refer to a name of class or function that is defined within a namespace?
Ans: There are two ways in which we can refer to a name of class or function that is defined within a namespace: Using scope resolution operator through the using keyword. This is shown in following example: namespace name1 { class sample1 { // code } ; } namespace name2 { class sample2 { // code } ; } using namespace name2 ; void main( ) { name1::sample1 s1 ; sample2 s2 ; }Here, class sample1 is referred using the scope resolution operator. On the other hand we can directly refer to class sample2 because of the statement using namespace name2 ; the using keyword declares all the names in the namespace to be in the current scope. So we can use the names without any qualifiers.
While overloading a binary operator can we provide default values?
Ans: No!. This is because even if we provide the default arguments to the parameters of the overloaded operator function we would end up using the binary operator incorrectly. This is explained in the following example: sample operator + ( sample a, sample b = sample (2, 3.5f ) ) { }
-------------------------------------------------------------------------------------------------9.How do I carry out conversion of one object of user-defined type to another?
Ans: To perform conversion from one user-defined type to another we need to provide conversion function. Following program demonstrates how to provide such conversion function. class circle { private : int radius ; public: circle ( int r = 0 ) { radius = r ; } } ; class rectangle { private : int length, breadth ; public : rectangle( int l, int b ) { length = l ; breadth = b ; } operator circle( ) { return circle ( length ) ; }
} ; void main( ) { rectangle r ( 20, 10 ) ; circle c; c = r ; }Here, when the statement c = r ; is executed the compiler searches for an overloaded assignment operator in the class circle which accepts the object of type rectangle. Since there is no such overloaded assignment operator, the conversion operator function that converts the rectangle object to the circle object is searched in the rectangle class. We have provided such a conversion function in the rectangle class. This conversion operator function returns a circle object. By default conversion operators have the name and return type same as the object type to which it converts to. Here the type of the object is circle and hence the name of the operator function as well as the return type is circle.-------------------------------------------------------------------------------------------------10.How do I write code that allows to create only one instance of a class?
Ans: This is shown in following code snippet.
#include class sample { static sample *ptr ; private: sample( ) { } public: static sample* create( ) { if ( ptr == NULL ) ptr = new sample ; return ptr ; } } ; sample *sample::ptr = NULL ; void main( ) { sample *a = sample::create( ) ; sample *b = sample::create( ) ; }Here, the class sample contains a static data member ptr, which is a pointer to the object of same class. The constructor is private which avoids us from creating objects outside the class. A static member function called create( ) is used to create an object of the class. In this function the condition
is checked whether or not ptr is NULL, if it is then an object is created dynamically and its address collected in ptr is returned. If ptr is not NULL, then the same address is returned. Thus, in main( ) on execution of the first statement one object of sample gets created whereas on execution of second statement, b holds the address of the first object. Thus, whatever number of times you call create( ) function, only one object of sample class will be available.
11.
How do I write code to add functions, which would work as get and put properties of a class?
Ans: This is shown in following code. #include
class sample { int data ; public: __declspec ( property ( put = fun1, get = fun2 ) ) int x ; void fun1 ( int i ) { if ( i < 0 ) data = 0 ; else data = i ; } int fun2( ) { return data ; } } ;
void main( ) { sample a ; a.x = -99 ; cout << a.x ; }Here, the function fun1( ) of class sample is used to set the given integer value into data, whereas fun2( ) returns the current value of data. To set these functions as properties of a class we have given the statement as shown below: __declspec ( property ( put = fun1, get = fun2 )) int x ;As a result, the statement a.x = -99 ; would cause fun1( ) to get called to set the value in data. On the other hand, the last statement would cause fun2( ) to get called to return the value of data.
How do I write code to make an object work like a 2-D array?
Ans: Take a look at the following program.
#include class emp { public : int a[3][3] ; emp( ) { int c = 1 ; for ( int i = 0 ; i <= 2 ; i++ ) { for ( int j = 0 ; j <= 2 ; j++ ) { a[i][j] = c ; c++ ; } } }
int* operator[] ( int i ) { return a[i] ; } } ;
void main( ) { emp e ; cout << e[0][1] ; }The class emp has an overloaded operator [ ] function. It takes one argument an integer representing an array index and returns an int pointer. The statement cout << e[0][1] ; would getconverted into a call to the overloaded [ ] function as e.operator[ ] ( 0 ). 0 would get collected in i. The function would return a[i] that represents the base address of the zeroeth row. Next the statement would get expanded as base address of zeroeth row[1] that can be further expanded as *( base address + 1 ). This gives us a value in zeroth row and first column.
13.What are formatting flags in ios class?
Ans: The ios class contains formatting flags that help users to format the stream data. Formatting flags are a set of enum definitions. There are two types of formatting flags: On/Off flags Flags that work in-group
The On/Off flags are turned on using the setf( ) function and are turned off using the unsetf( ) function. To set the On/Off flags, the one argument setf( ) function is used. The flags working in groups are set through the two-argument setf( ) function. For example, to left justify a string we can set the flag as, cout.setf ( ios::left ) ; cout << "KICIT Nagpur" ;To remove the left justification for subsequent output we can say, cout.unsetf ( ios::left ) ;The flags that can be set/unset include skipws, showbase, showpoint, uppercase, showpos, unitbuf and stdio. The flags that work in a group can have only one of these flags set at a time.
14.What is the purpose of ios::basefield in the following statement?
cout.setf ( ios::hex, ios::basefield ) ; Ans: This is an example of formatting flags that work in a group. There is a flag for each numbering system (base) like decimal, octal and hexadecimal. Collectively, these flags are referred to as basefield and are specified by ios::basefield flag. We can have only one of these flags on at a time. If we set the hex flag as setf ( ios::hex ) then we will set the hex bit but we won't clear the dec bit resulting in undefined behavior. The solution is to call setf( ) as setf ( ios::hex, ios::basefield ). This call first clears all the bits and then sets the hex bit.-------------------------------------------------------------------------------------------------15.Can we get the value of ios format flags?
Ans: Yes! The ios::flags( ) member function gives the value format flags. This function takes no arguments and returns a long ( typedefed to fmtflags) that contains the current format flags.
-------------------------------------------------------------------------------------------------16.Is there any function that can skip certain number of characters present in the input stream?
Ans: Yes! This can be done using cin::ignore( ) function. The prototype of this function is as shown below: istream& ignore ( int n = 1, int d =EOF ) ;Sometimes it happens that some extra characters are left in the input stream while taking the input such as, the '\n' (Enter) character. This extra character is then
passed to the next input and may pose problem.
To get rid of such extra characters the cin::ignore( ) function is used. This is equivalent to fflush ( stdin ) used in C language. This function ignores the first n characters (if present) in the input stream, stops if delimiter d is encountered.
Write a program that implements a date class containing day, month and year as data members. Implement assignment operator and copy constructor in this class.
Ans: This is shown in following program: #include
class date { private : int day ; int month ; int year ; public : date ( int d = 0, int m = 0, int y = 0 ) { day = d ; month = m ; year = y ; }
// copy constructor date ( date &d ) { day = d.day ; month = d.month ; year = d.year ; }
// an overloaded assignment operator date operator = ( date d ) { day = d.day ; month = d.month ; year = d.year ; return d ; } void display( ) { cout << day << "/" << month << "/" << year ; } } ;
void main( ) { date d1 ( 25, 9, 1979 ) ; date d2 = d1 ; date d3 ; d3 = d2 ; d3.display( ) ; }
18.When should I use unitbuf flag?
Ans: The unit buffering (unitbuf) flag should be turned on when we want to ensure that each character is output as soon as it is inserted into an output stream. The same can be done using unbuffered output but unit buffering provides a better performance than the unbuffered output.-------------------------------------------------------------------------------------------------19.
What are manipulators?Ans: Manipulators are the instructions to the output stream to modify the output in various ways. The manipulators provide a clean and easy way for formatted output in comparison to the formatting flags of the ios class. When manipulators are used, the formatting instructions are inserted directly into the stream. Manipulators are of two types, those that take an argument and those that don't.-------------------------------------------------------------------------------------------------20.
What is the difference between the manipulator and setf( ) function?
Ans: The difference between the manipulator and setf( ) function are as follows:The setf( ) function is used to set the flags of the ios but manipulators directly insert the formatting instructions into the stream. We can create user-defined manipulators but setf( ) function uses data members of ios class only. The flags put on through the setf( ) function can be put off through unsetf( ) function. Such flexibility is not available with manipulators.-------------------------------------------------------------------------------------------------21.How do I get the current position of the file pointer?Ans: We can get the current position of the file pointer by using the tellp( ) member function of ostream class or tellg( ) member function of istream class. These functions return (in bytes) positions of put pointer and get pointer respectively.
-------------------------------------------------------------------------------------------------22.What are put and get pointers?
Ans: These are the long integers associated with the streams. The value present in the put pointer specifies the byte number in the file from where next write would take place in the file. The get pointer specifies the byte number in the file from where the next reading should take place.-------------------------------------------------------------------------------------------------23.What do the nocreate and noreplace flag ensure when they are used for opening a file?
Ans: nocreate and noreplace are file-opening modes. A bit in the ios class defines these modes. The flag nocreate ensures that the file must exist before opening it. On the other hand the flag noreplace ensures that while opening a file for output it does not get overwritten with new one unless ate or app is set. When the app flag is set then whatever we write gets appended to the existing file. When ate flag is set we can start reading or writing at the end of existing file.-------------------------------------------------------------------------------------------------24.What is the limitation of cin while taking input for character array?
Ans: To understand this consider following statements, char str[5] ; cin >> str ;While entering the value for str if we enter more than 5 characters then there is no provision in cin to check the array bounds. If the array overflows, it may be dangerous. This can be avoided by using get( ) function. For example, consider following statement, cin.get ( str, 5 ) ;
On executing this statement if we enter more than 5 characters, then get( ) takes only first five characters and ignores rest of the characters. Some more variations of get( ) are available, such as shown below:
get ( ch ) - Extracts one character only
get ( str, n ) - Extracts up to n characters into str
get ( str, DELIM ) - Extracts characters into array str until specified delimiter (such as '\n'). Leaves delimiting character in stream.
get ( str, n, DELIM ) - Extracts characters into array str until n characters or DELIM character, leaving delimiting character in stream.-------------------------------------------------------------------------------------------------25.
What is the purpose of istream class?
Ans: The istream class performs activities specific to input. It is derived from the ios class. The most commonly used member function of this class is the overloaded >> operator which can extract values of all basic types. We can extract even a string using this operator.-------------------------------------------------------------------------------------------------26.
Would the following code work? #include void main( ) { ostream o ; o << "Dream. Then make it happen!" ; }Ans: No! This is because we cannot create an object of the ostream class since its constructor and copy constructor are declared private.
27.Can we use this pointer inside static member function?
Ans: No! The this pointer cannot be used inside a static member function. This is because a static member function is never called through an object.-------------------------------------------------------------------------------------------------28.What is strstream?
Ans: strstream is a type of input/output stream that works with the memory. It allows using section of the memory as a stream object. These streams provide the classes that can be used for storing the stream of bytes into memory. For example, we can store integers, floats and strings as a stream of bytes. There are several classes that implement this in-memory formatting. The class ostrstream derived from ostream is used when output is to be sent to memory, the class istrstream derived from istream is used when input is taken from memory and strstream class derived from iostream is used formemory objects that do both input and output.
Ans: When we want to retrieve the streams of bytes from memory we can use istrestream. The following example shows the use of istrstream class. #include
void main( ) { int age ; float salary ; char name[50] ; char str[] = "22 12004.50 K. Vishwanatth" ;
istrstream s ( str ) ; s >> age >> salary >> name ;
cout << age << endl << salary << endl << name ; cout << endl << s.rdbuf( ) ; }Here, s is the object of the class istrstream. When we are creating the object s, the constructor of istrstream gets called that receives a pointer to the zero terminated character array str. The statement s >> age >> salary >> name ; extracts the age, salary and the name from the istrstream object s. However, while extracting the name, only the first word of name gets extracted. The balance is extracted using rdbuf( ).
-------------------------------------------------------------------------------------------------30.When the constructor of a base class calls a virtual function, why doesn't the override function of the derived class gets called?
Ans: While building an object of a derived class first the constructor of the base class and then the constructor of the derived class gets called. The object is said an immature object at the stage when the constructor of base class is called. This object will be called a matured object after the execution of the constructor of the derived class. Thus, if we call a virtual function when an object is still immature, obviously, the virtual function of the base class would get called. This is illustrated in the following example. #include
class base { protected : int i ; public : base ( int ii = 0 ) { i = ii ;
class derived : public base { private : int j ; public : derived ( int ii, int jj = 0 ) : base ( ii ) { j = jj ; show( ) ; } void show( ) { cout << "derived's show( )" << endl ; } } ; void main( ) { derived dobj ( 20, 5 ) ; } The output of this program would be: base's show( ) derived's show( )
31.Can I have a reference as a data member of a class? If yes, then how do I initialise it?
Ans: Yes, we can have a reference as a data member of a class. A reference as a data member of a class is initialised in the initialisation list of the constructor. This is shown in following program. #include
class sample { private : int& i ; public : sample ( int& ii ) : i ( ii ) { }
void show( ) { cout << i << endl ; } } ;
void main( ) { int j = 10 ; sample s ( j ) ; s.show( ) ; }Here, i refers to a variable j allocated on the stack. A point to note here is that we cannot bind a reference to an object passed to the constructor as a value. If we do so, then the reference i would refer to the function parameter (i.e. parameter ii in the constructor), which would disappear as soon as the function returns, thereby creating a situation of dangling reference.-------------------------------------------------------------------------------------------------32.Why does the following code fail?
#include
class sample { private : char *str ; public : sample ( char *s ) { strcpy ( str, s ) ; }
~sample( ) { delete str ; } } ;
void main( ) { sample s1 ( "abc" ) ; }Ans: Here, through the destructor we are trying to deal locate memory, which has been allocated statically. To remove an exception, add following statement to the constructor. sample ( char *s ) { str = new char[strlen(s) + 1] ; strcpy ( str, s ) ; }Here, first we have allocated memory of required size, which then would get deal located through the destructor.-------------------------------------------------------------------------------------------------33.assert( ) macro...
We can use a macro called assert( ) to test for conditions that should not occur in a code. This macro expands to an if statement. If test evaluates to 0, assert prints an error message and calls abort to abort the program. #include #include
void main( ) { int i ;
cout << "\nEnter an integer: " ; cin >> i ;
assert ( i >= 0 ) ; cout << i << endl ; }
34.Why it is unsafe to deal locate the memory using free( ) if it has been allocated using new?Ans: This can be explained with the following example: #include
class sample { int *p ; public : sample( ) { p = new int ; }
sample *s2 = ( sample * ) malloc ( sizeof ( sample ) ) ; delete s2 ; }The new operator allocates memory and calls the constructor. In the constructor we have allocated memory on heap, which is pointed to by p. If we release the object using the free( ) function the object would die but the memory allocated in the constructor would leak. This is because free( ) being a C library function does not call the destructor where we have deal located the memory.
As against this, if we allocate memory by calling malloc( ) the constructor would not get called. Hence p holds a garbage address. Now if the memory is deal located using delete, the destructor would get called where we have tried to release the memory pointed to by p. Since p contains garbage this may result in a runtime error.-------------------------------------------------------------------------------------------------
35.Can we distribute function templates and class templates in object libraries?
Ans: No! We can compile a function template or a class template into object code (.obj file). The code that contains a call to the function template or the code that creates an object from a class template can get compiled. This is because the compiler merely checks whether the call matches the declaration (in case of function template) and whether the object definition matches class declaration (in case of class template). Since the function template and the class template definitions are not found, the compiler leaves it to the linker to restore this. However, during linking, linker doesn't find the matching definitions for the function call or a matching definition for object creation. In short the expanded versions of templates are not found inthe object library. Hence the linker reports error.-------------------------------------------------------------------------------------------------36.What is the difference between an inspector and a mutator ? Ans: An inspector is a member function that returns information about an object's state (information stored in object's data members) without changing the object's state. A mutator is a member function that changes the state of an object. In the class Stack given below we have defined a mutator and an inspector. class Stack { public : int pop( ) ; int getcount( ) ; } In the above example, the function pop( ) removes top element of stack thereby changing the state of an object. So, the function pop( ) is a mutator. The function getcount( ) is an inspector because it simply counts the number of elements in the stack without changing the stack.
37.
Namespaces:
The C++ language provides a single global namespace. This can cause problems with global name clashes. For instance, consider these two C++ header files: // file1.h float f ( float, int ) ; class sample { ... } ; // file2.h class sample { ... } ; With these definitions, it is impossible to use both header files in a single program; the sample classes will clash.A namespace is a declarative region that attaches an additional identifier to any names declared inside it. The additional identifier thus avoids the possibility that a name will conflict with names declared elsewhere in the program. It is possible to use the same name in separate namespaces without conflict even if the names appear in the same translation unit. As long as they appear in separate namespaces, each name will be unique because of the addition of the namespace identifier. For example: // file1.h namespace file1 { float f ( float, int ) ; class sample { ... } ; } // file2.h namespace file2 { class sample { ... } ; } Now the class names will not clash because they become file1::sample and file2::sample, respectively.-------------------------------------------------------------------------------------------------38.What would be the output of the following program?
#includeclass user{int i ;float f ;char c ;public :void displaydata( ){cout << endl << i << endl << f << endl << c ;}} ;
Since the user class contains three elements, int, float and char its size would be 9 bytes (int-4, float-4, char-1) under Windows and 7 bytes (int-2, float-4, char-1) under DOS. Second output is again the same because u1 is an object of the class user. Finally three garbage values are printed out because i, f and c are not initialized anywhere in the program.
Note that if you run this program you may not get the answer shown here. This is because packing is done for an object in memory to increase the access efficiency. For example, under DOS, the object would be aligned on a 2-byte boundary. As a result, the size of the object would be reported as 6 bytes. Unlike this, Windows being a 32-bit OS the object would be aligned on a 4-byte boundary. Hence the size of the object would be reported as 12 bytes. To force the alignment on a 1-byte boundary, write the following statement before the class declaration.#pragma pack ( 1 )-------------------------------------------------------------------------------------------------39.
Write a program that will convert an integer pointer to an integer and vice-versa.
Ans: The following program demonstrates this. #include void main( ) { int i = 65000 ;
int *iptr = reinterpret_cast ( i ) ; cout << endl << iptr ;
iptr++ ; cout << endl << iptr ;
i = reinterpret_cast ( iptr ) ; cout << endl << i ;
i++ ; cout << endl << i ;
}
40.What is a const_cast?
Ans. The const_cast is used to convert a const to a non-const. This is shown in the following program: #include void main( ) { const int a = 0 ; int *ptr = ( int * ) &a ; //one way ptr = const_cast_ ( &a ) ; //better way }Here, the address of the const variable a is assigned to the pointer to a non-const variable. The const_cast is also used when we want to change the data members of a class inside the const member functions. The following code snippet shows this: class sample { private: int data; public: void func( ) const { (const_cast (this))->data = 70 ; } } ;-------------------------------------------------------------------------------------------------41.What is forward referencing and when should it be used?Ans: Forward referencing is generally required when we make a class or a function as a friend.Consider following program: class test { public: friend void fun ( sample, test ) ; } ;
class sample { public: friend void fun ( sample, test ) ; } ;
void fun ( sample s, test t ) { // code }
void main( ) { sample s ; test t ;
fun ( s, t ) ; }On compiling this program it gives error on the following statement of test class. It gives an error that sample is undeclared identifier. friend void fun ( sample, test ) ;This is so because the class sample is defined below the class test and we are using it before its definition. To overcome this error we need to give forward reference of the class sample before the definition of class test. The following statement is the forward reference of class sample.class sample ;-------------------------------------------------------------------------------------------------42.How would you give an alternate name to a namespace?
Ans: An alternate name given to namespace is called a namespace-alias. namespace-alias is generally used to save the typing effort when the names of namespaces are very long or complex. The following syntax is used to give an alias to a namespace. namespace myname = my_old_very_long_name ;
-------------------------------------------------------------------------------------------------43.Using a smart pointer can we iterate through a container?
Ans: Yes. A container is a collection of elements or objects. It helps to properly organize and store the data. Stacks, linked lists, arrays are examples of containers. Following program shows how to iterate through a container using a smart pointer. #include
class smartpointer { private : int *p ; // ordinary pointer public : smartpointer ( int n ) { p = new int [ n ] ; int *t = p ; for ( int i = 0 ; i <= 9 ; i++ ) *t++ = i * i ; }
int* operator ++ ( int ) { return p++ ; }
int operator * ( ) { return *p ; }
} ;
void main( ) { smartpointer sp ( 10 ) ;
for ( int i = 0 ; i <= 9 ; i++ ) cout << *sp++ << endl ; }Here, sp is a smart pointer. When we say *sp, the operator * ( ) function gets called. It returns the integer being pointed to by p. When we say sp++ the operator ++ ( ) function gets called. It increments p to point tothe next element in the array and then returns the address of this new location.
44.Can objects read and write themselves?
Ans: Yes! This can be explained with the help of following example:
#include #include
class employee { private : char name [ 20 ] ; int age ; float salary ; public : void getdata( ) { cout << "Enter name, age and salary of employee : " ; cin >> name >> age >> salary ; }
for ( int i = 0 ; i <= 4 ; i++ ) { e [ i ].getdata( ) ; e [ i ].store( ) ; }
for ( i = 0 ; i <= 4 ; i++ ) { e [ i ].retrieve ( i ) ; e [ i ].show( ) ; } }Here, employee is the class whose objects can write and read themselves. The getdata( ) function has been used to get the data of employee and store it in the data members name, age and salary. The store( ) function is used to write an object to the file. In this function a file has been opened in append mode and each time data of current object has been stored after the last record (if any) in the file.Function retrieve( ) is used to get the data of a particular employee from the file. This retrieved data has been stored in the data members name, age and salary. Here this has been used to store data since it contains the address of the current object. The function show( ) has been used to display the data of employee.-------------------------------------------------------------------------------------------------45.Why is it necessary to use a reference in the argument to the copy constructor?
Ans : If we pass the copy constructor the argument by value, its copy would get constructed using the copy constructor. This means the copy constructor would call itself to make this copy. This process would go on and on until the compiler runs out of memory. This can be explained with the help of following example: class sample { int i ; public : sample ( sample p ) { i = p.i ; } } ;
void main( ) {
sample s ; sample s1 ( s ) ; }While executing the statement sample s1 ( s ), the copy constructor would get called. As the copy construct here accepts a value, the value of s would be passed which would get collected in p. We can think of this statement as sample p = s. Here p is getting created and initialized. Means again the copy constructor would get called. This would result into recursive calls. Hence we must use a reference as an argument in a copy constructor. 46.Virtual Multiple Inheritance:A class b is defined having member variable i. Suppose two classes d1 and d2 are derived from class b and a class multiple is derived from both d1 and d2. If variable i is accessed from a member function of multiple then it gives error as 'member is ambiguous'. To avoid this error derive classes d1 and d2 with modifier virtual as shown in the following program. #include class b { public : int i ; public : fun( ) { i = 0 ; } } ; class d1 : virtual public b { public : fun( ) { i = 1 ; } } ; class d2 : virtual public b { public : fun( ) { i = 2 ; } } ; class multiple : public d1, public d2 { public : fun( ) { i = 10 ; } } ; void main( ) { multiple d ;
Can we use this pointer in a class specific, operator-overloading function for new operator?
Ans: No! The this pointer is never passed to the overloaded operator new() member function because this function gets called before the object is created. Hence there is no question of the this pointer getting passed to operator new( ).-------------------------------------------------------------------------------------------------48.Can we allocate memory dynamically for a reference?
Ans: No! It is not possible to allocate memory dynamically for a reference. This is because, when we create a reference, it gets tied with some variable of its type. Now, if we try to allocate memory dynamically for a reference, it is not possible to mention that to which variable the reference would get tied.
49.When should I overload new operator on a global basis or a class basis?
Ans: We overload operator new in our program, when we want to initialize a data item or a class object at the same place where it has been allocated memory. The following example shows how to overload new operator on global basis.
#include #include
void * operator new ( size_t s ) { void *q = malloc ( s ) ; return q ; }
void main( ) { int *p = new int ; *p = 25 ; cout << *p ; }When the operator new is overloaded on global basis it becomes impossible to initialize the data members of a class as different classes may have different types of data members. The following example shows how tooverload new operator on class-by-class basis. #include #include
class sample { int i ;
public : void* operator new ( size_t s, int ii ) { sample *q = ( sample * ) malloc ( s ) ; q -> i = ii ; return q ; } } ;
class sample1 { float f ; public : void* operator new ( size_t s, float ff ) { sample1 *q = ( sample1 * ) malloc ( s ) ; q -> f = ff ; return q ; } } ;
void main( ) { sample *s = new ( 7 ) sample ; sample1 *s1 = new ( 5.6f ) sample1 ; }Overloading the operator new on class-by-class basis makes it possible to allocate memory for an object and initialize its data members at the same place.-------------------------------------------------------------------------------------------------50.How would you define a pointer to a data member of the type pointer to pointer?
Ans: The following program demonstrates this... #include
class sample { public : sample ( int **pp ) { p = pp ; } int **p ; } ; int **sample::*ptr = &sample::p ;
void main( ) { int i = 9 ; int *pi = &i ;
sample s ( π ) ; cout << ** ( s.*ptr ) ; }Here, ptr is the pointer to data member p of class sample, which in turn is a pointer pointing to an int.-------------------------------------------------------------------------------------------------51.How do I write a code to catch multiple types of exceptions in one single catch block?
Ans: The following program demonstrates the use of a single catch block to catch multiple exceptions.
void main( ) { try { sample s ; s.fun4( ) ; s.fun1( ) ; s.fun2( ) ; s.fun3( ) ; } catch ( ... ) { cout << "strange" ; } }Here, different types of exceptions are thrown by the member functions of the class sample. While catching the
exception instead of four different catch blocks we can as well define one single catch block. Note the syntax for defining the catch block, where we have used three dots (…) in the formal parameter list. This indicates that any thrown exception should get caught in the same catch block. When the exception is thrown from the fun4( ) control reaches the catch block, ignoring the rest of the calls.
52. Can we return an error value from the constructor of a class?
Ans: No. We cannot return any error value from the constructor, as the constructor doesn't have any return type. However, by throwing an exception we can pass value to catch block. This is shown in the following example: #include
class sample { public : sample ( int i ) { if ( i == 0 ) throw "error" ; } } ;
void main( ) { try { sample s ( 0 ) ; } catch ( char * str ) { cout << str ; } }In this program, the statement throw "error" ; would throw an exception when an object s of the class sample would get created. The catch block would collect the string error.-------------------------------------------------------------------------------------------------53.
How do I define the member function of a template class, which has to be defined outside the template class. The function receives an object of its own class as a parameter and returns the value of the same type.
Ans: The following example shows how we can define such a function. sample sample::fun ( sample s ) { // code }
Here, the first sample indicates the return type of the function and the next sample is used for the scope of function.-------------------------------------------------------------------------------------------------54.How name mangling can be prevented?
Ans: To avoid name mangling the function should be declared with an extern "C" attribute. Functions declared as extern "C" are treated as C-style functions. Hence the compiler does not mangle them. The following code snippet shows how to declare such a function. #include
extern "C" void display( ) { cout << "See the effect of C in C++ " ; }
void main( ) { display( ) ; }-------------------------------------------------------------------------------------------------55.Can we allocate memory dynamically for a reference?
Ans: No, it is not possible to allocate memory dynamically for a reference. A reference is initialized at the time of creation. Trying to allocate memory dynamically for a reference creates a problem in initializing it. Thus, the compiler does not allow us to dynamically allocate the memory for references. -------------------------------------------------------------------------------------------------56.What is RTTI? Ans: RTTI stands for 'Run Time Type Information'. We use virtual function mechanism where we can call derived class's member functions using base class's pointer. However, many times we wish to know the exact type of the object. We can know the type of the object using RTTI. A function that returns the type of the object is known as RTTI functions. C++ supports two ways to obtain information about the object's class at run time, they are typeid( ) operator and dynamic_cast operator.
57.
What is Data Conversion?Ans: Assignments between types whether they are basic or user-defined, are handled by the compiler. If the variables are of different basic types compiler calls a special routine to convert the value. But if we want to convert between user-
defined data type and basic types we have to write conversion routine ourselves. A conversion routine to convert user-defined data type string to integer is shown below: class string { private : char str[20] ; public : string( ) { } string ( char *s ) { strcpy ( str, s ) ; } operator int( ) { return 123 ; // Write logic to convert string to integer } } ; main( ) { string s2 = "123" ; int i1 = int ( s2 ) ; cout << endl << i1 ; }-------------------------------------------------------------------------------------------------
58.How to obtain type information using typeid( ) operator? Ans: typeid( ) operator takes an object, a reference or a pointer and returns its type. Following program shows how to use the typeid( ) operator. #include #include class Base { public : virtual void show( ) { } }; class Der1 : public Base { } ; void main( ) { Base *b1 ;
cout << endl << typeid ( b1 ).name( ) ; Der1 d1 ; b1 = &d1 ; cout << endl << typeid ( *b1 ).name( ) ; cout << endl << typeid ( 12 ).name( ) << endl << typeid ( 12.5 ).name( ) ; } The output of this program will be Base* Der1 int double RTTI operators must be used for polymorphic class (class having virtual function) only. For non-polymorphic class static type information is returned.-------------------------------------------------------------------------------------------------59.How to use RTTI with class templates? Ans: Templates can generate different classes. We may wish to get the type of class, which we are working in. The following program shows how to use RTTI operator typeid( ) with class template. #include #include template class base { public : base( ) { cout << typeid ( *this ).name( ) << "Constructor" << endl ; } T add ( T a, T b ) { return a + b ; } ~base( ) { cout << typeid ( *this ).name( ) << "Destructor" << endl ; } } ; void main( ) { base b1 ; cout << b1.add ( 10, 20 ) << endl ;
60.We can use following C++ operators for typecasting.static_cast is used for castless conversions, narrowing conversions, conversion from void* and implicit type conversions. const_cast is used to convert a const to a non-const. reinterpret_cast is used to assign one kind of pointer to another.-------------------------------------------------------------------------------------------------61.What will be the output of the following program? #include class A { public : A( ) { cout << "Reached in Constructor\n" ; } } ; void main( ) { A a( ) ; A b ; } Output : Reached in Constructor Constructor gets called only once when the object b is created. When the statement A a( ) ; gets executed constructor does not get called. This is because compiler takes this statement as a prototype declaration of function a( ) that returns an object of class A. However, if we pass arguments like A a ( 10 ) ;Compiler would search for one argument constructor and if not found would flash an error.-------------------------------------------------------------------------------------------------62.
What is a container?
Ans: A container is an object that holds other objects. Various collection classes like List, Hash Table, AbstractArray, etc. are the examples of containers. We can use the classes to hold objects of any derived classes. The containers provide various methods using which we can get the number of objects stored in the container and iterate through the objects stored in it.
Function template overloading One can declare several function templates with the same name and even declare a combination of function templates and ordinary functions with the same name. When an overloaded function is called, overload resolution is necessary to find the right function or template function to invoke. For example: template < class T > T sqrt ( T ) ; template < class T > complex < T > sqrt ( complex < T > ) ;double sqrt ( double ) ; void f ( complex < double > z ) { sqrt ( 2 ) ; // sqrt < int > ( int ) sqrt ( 2.0 ) ; // sqrt ( double ) sqrt ( z ) ; // sqrt < complex < double > ( complex < double > ) }In the same way that a template function is a generalization of the notion of a function, the rules for resolution in the presence of function templates are generalizations of the function overload resolution rules. Basically, for each template we find the specialization that is best for the set of function arguments. Then we apply the usual function overload resolution rules to these specializations and all ordinary functions.
64.Exception Handling in C++ In C++ we can handle run-time errors generated by c++ classes by using three new keywords: throw, catch, and try. We also have to create an exception class. If during the course of execution of a member function ofthis class a run-time error occurs, then this member function informs the application that an error has occurred. This process of informing is called 'throwing' an exception. The following code shows how to deal with exception handling. class sample { public : class errorclass { } ; void fun( ) { if ( some error occurs ) throw errorclass( ) // throws exception } } ; //application
void main( ) { try { sample s ; s.fun( ) ; } catch ( sample::errorclass ) { // do something about the error } }-------------------------------------------------------------------------------------------------65.Consider the following code: #include class base { public : int data ; } ; class d1 : public base { } ; class d2 : public base { } ; class der : public d1, public d2 { public : void showdata( ) { cout << data ; } } ; void main( ) { der d ; d.showdata( ) ; } If you run this program it is bound to give you errors. This is because of the rules of inheritance: 1. Each base class not specified virtual will have its own sub-object representing it. In the above program, if we create object of d1 it will have a sub-object of class base containing a data member data. If we create an object of class der it will have sub-objects of classes d1 and d2 and both the sub-objects will refer to a separate copy of data. Hence, to access data from class der we will have to mention the class name. For example, d1::data or d2::data.
2. If we want that only one sub-object should exist we must use the concept of virtual base class. The single object of this will represent every base class of given name that is specified to be virtualclass. After making d1 and d2 as virtual base class if we create an object of der only one sub-object would exist and so accessing data would no longer give us errors.-------------------------------------------------------------------------------------------------66.How to declare a pointer to a member function? Ans: Suppose, I wish to declare a pointer to a member function that receives an int and returns an int. I will have to declare it as int (A::* ) ( int ). Following is an example. #include class A { public : int fun ( int f ) { cout << "in fun\n" ; return f * f ; } } ; typedef int ( A:: *pfun ) ( int ) ; void main( ) { pfun p = A::fun ; A a ; int s = ( a.*p ) ( 6 ) ; cout << s ; }
67.What is the disadvantage of a template function? Ans: A template function cannot be distributed in the obj form. This is because, with which parameters the template function is going to be called is decided at the run time only. Therefore an obj form of a template function cannot be made by merely compiling it.-------------------------------------------------------------------------------------------------68.
How to declare a pointer to the data members of a class? Ans: Following program shows how to declare a pointer to non-function members of a class.
#include class A { public : int a ; void print( ) { cout << a ; } } ; void main( ) { int A::*pa = &A::a ; A obj ; obj.*pa = 20 ; obj.print( ) ; } Here, we have initialised the data member a using the pointer pa.-------------------------------------------------------------------------------------------------
69.How to allocate memory for a multidimensional array dynamically? Ans: Many times we need to allocate memory for a multidimensional array dynamically. Because of complexity of pointers many find this difficult. Following program allocates memory for a 3 x 3 array dynamically, copies contents of a 3 x 3 array in it and prints the contents using the pointer. #include #include int a[ ][3] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 } ; void main( ) { int **p ; p = new int *[3] ; for ( int i = 0 ; i < 3 ; i++ ) p[i] = new int[3] ; for ( i = 0 ; i < 3 ; i++ ) for ( int j = 0 ; j < 3 ; j++ ) p[i][j] = a[i][j] ;
for ( i = 0 ; i < 3 ; i++ ) { for ( j = 0 ; j < 3 ; j++ ) cout << p[i][j] ; cout << "\n" ; } }
70.When should we use the :: ( scope resolution ) operator to invoke the virtual functions? Ans: Generally, :: operator is used to call a virtual function from constructor or destructor. This is because, if we call a virtual function from base class constructor or destructor the virtual function of the base class would get called even if the object being constructed or destroyed would be the object of the derived class. Thus, whenever we want to bypass the dynamic binding mechanism we must use the :: operator to call a virtual function.-------------------------------------------------------------------------------------------------71.How do I use operators .* and ->* in a program?
Ans: The following code snippet demonstrates the use of .* and ->* operators.
#include
class sample { public : int i ; void fun( ) { cout << "fun" << endl ; } } ;
void main( ) { sample s ; sample *p = new sample ;
( s .* pf )( ) ; ( p ->* pf )( ) ;
s .* pdm = 1 ; p ->* pdm = 2 ;
cout << s .* pdm << endl ;
cout << p ->* pdm << endl ; }In the above program pf is a pointer to a function fun( ) of class sample, and pdm is a pointer to a data member i of the same class sample. The object s of the class sample is created statically. Next, p is a pointer to an object created dynamically. The using the operator .* and ->* the member functions are called and also the public data member is accessed. -------------------------------------------------------------------------------------------------72.What happens when we add an int value to a user defined type of object?
Ans: Whenever an int value is added to an object of user defined type, the object would search for an overloaded operator int( ). This operator must be defined in such a way that it always returns an int value. However, we need not specify the return type as on doing so the compiler flashes an error.
#include class sample { int i ;
public : sample ( ) { i = 10 ; } operator int( ) { return this -> i ; } } ; void main( ) { sample s ; int i ; i = s + 10 ; cout << i ; } In the above program on adding 10 to an object s, the value of i would become 2073.Can we have a reference to an array?Ans: Yes, we can have a reference to an array.
int a[ ] = { 8, 2, 12, 9 } ; int ( &r ) [ 4 ] = a ; // reference to an array
Here, r is a reference to an array of four elements. We can even print the elements of array with the help of reference. This is shown in the following code segment:
for ( int i = 0 ; i < 4 ; i++ ) cout << r [i] << endl ;-------------------------------------------------------------------------------------------------74.When friend function becomes indispensable... Ans: Consider the following program. #include class distance { private : int feet ; public : distance( ) { feet = 0 ; } distance ( int f ) { feet = f ; } distance operator + ( distance x ) { int f = feet + x.feet ; return distance ( f ) ; } } ; void main( ) { distance d1 ( 20 ), d2, d3 ; d2 = d1 + 10 ; d3 = 10 + d2 ; } If you run this program it is bound to give errors. The error lies in the statement d3 = 10 + d2 ; We may think that since we have overloaded + operator this statement would add 10 to d2. But this does not happen. This is because the specified statement will get converted as d3 = 10.operator+ ( d2 ) ; This means that this statement should call the operator+( ) function that takes an object of distance class as parameter written inthe float class, which is not possible. The solution is to write operator+( ) as a 'friend' function. Declare operator+ function in distance class as given below: friend distance operator + ( distance x1, distance x2 ) ; and define it outside the class as shown below: distance operator + ( distance x1, distance x2 ) { int f = x1.feet + x2.feet ; return distance ( f ) ; }
When compiler would see that the 'friend' operator+( ) function is available it would convert the statement d3 = 10 + d2 as operator+ (10, d2 ). Now since 10 is passed as a parameter not as a calling object there would be no error. Thus in such cases 'friend' function becomes indispensable. -------------------------------------------------------------------------------------------------75.How to use a memory as a stream? Ans: Suppose, details of an employee such as name, designation, age, etc. are stored in different types of variables. Now, if we wish to concatenate these details in a character array we will have to use various string manipulation functions like strcpy( ) and strcat( ). Instead of using these functions we can use more easy and clean way to gather the details in the char array in the form of streams. We can declare the memory allocated for the array as stream and use the << operator to store variables having different types in this memory. Following program shows how to achieve this. #include void main( ) { char buff [50] ; char str[ ] = "Sanjay" ; char desig[ ] = "Manager" ; char jd[ ] = "27/12/1995" ; int age = 35 ; ostrstream o ( buff, sizeof ( buff ) ) ; o << str << endl << desig << endl << jd << endl << age << ends ; cout << buff ; } As shown in the program we can also use the manipulators and formatting flags. The output of this program will be: Sanjay Manager 27/12/1995 35-------------------------------------------------------------------------------------------------
76.How would you declare and initialize reference to a data member?Ans: Sometimes we may need to declare a data member, which is a reference to another data member of the class as shown below: class A { public : char *p ; char *&rp ; } ;
We can't initialize a reference to a data member at the time of declaration. It should be initialized using 'member wise initialization as shown below. #include class A { public : char *p ; char *&rp ; A( ) : rp ( p ) { p = "" ; } A ( char *s ) : rp ( p ) { p = s ; } } ; void main( ) { A a ( "abcd" ) ; cout << a.rp ; } 77.iostream library has made it easy to read data from various input devices and write data to the output devices. The following program shows how to print a disk file 'data.dat' on the printer using stream classes. Every hardware device has a familiar name given by the operating system. The printer is generally connected to the first parallel port. So, the file name for the printer should be PRN or lpt1. #include void main( ) { ifstream i ( "data.dat" ) ; ofstream o ; o.open ( "PRN" ) ; char ch ; while ( 1 ) { i.get ( ch ) ; if ( i.eof( ) ) break ; o.put ( ch ) ; } o.put ( '\x0C' ) ; }-------------------------------------------------------------------------------------------------78. We know that a destructor is automatically called when an object of a class goes out of scope. There is another case where destructor is called automatically. If an object is
created in a try block and an exception is thrown after the object is created, then the destructor is called automatically.-------------------------------------------------------------------------------------------------79.Can a function call be at the left hand side of the assignment operator? Ans: Yes. Following program shows how it is possible. #include class ref { private : struct data { int a ; char *p ; } d1, d2 ; public : data &set ( ) { return d1 ; } data &get ( ) { cin >> d2.a >> d2.p ; return d2 ; } } ; void main( ) { ref r ; r.set( ) = r.get( ) ; r.print( ) ; }In the above program the functions get( ) and set( ) both return a reference to the object of the structure data. We have assigned the reference returned by get( ) to the reference returned by set( ) function. That is, we are assigning d2 to d1. So, the values of d2 would get assigned to d1. You can check this out by printing the values of d1.-------------------------------------------------------------------------------------------------
80.
If a class contains a virtual function a pointer called VPTR is created. This VPTR becomes a part of every object of that class. The first two bytes (in DOS) are occupied by VPTR. We can prove this by displaying the first two bytes of memory allocated for the objects. Following program shows how this can be achieved. #include class vir { public : virtual void f( )
{ } } ; void main( ) { vir v, v1 ; int *p1 = ( int* ) &v ; int *p2 = ( int* ) &v1 ; cout << endl << *p1 << " " << *p2 ; } 81.Exception Handling in C++ In C++ we can handle run-time errors generated by c++ classes by using three new keywords: throw, catch, and try. We also have to create an exception class. If during the course of execution of a member function ofthis class a run-time error occurs, then this member function informs the application that an error has occurred. This process of informing is called 'throwing' an exception. The following code shows how to deal with exception handling. class sample { public : class errorclass { } ; void fun( ) { if ( some error occurs ) throw errorclass( ) // throws exception } } ; //application void main( ) { try { sample s ; s.fun( ) ; } catch ( sample::errorclass ) { // do something about the error } }-------------------------------------------------------------------------------------------------82. Accessing a private data member from a different Object... Different objects of the same class can access each other's members, even if these members are private. For example:
#include < iostream.h > class sample { float f ; public : sample ( float ff ) { f = ff ; } void fun ( sample* objptr ) { objptr -> n = 0 ; cout << "Value of this objects f is : " << f << endl ; cout << "Value of other objects f" << objptr -> n << endl ; } // another object's private member! } ; void main( ) { sample s1 ( 6.5f ) , s2 ( 2.5f ) ; s1.f ( &s2 ) ; // s1 changes s2's n }Typically, this coding style should be avoided. However, you should be aware that private members of an object can be changed by another object of the same type. Therefore, in certain special conditions, this coding style may be useful.-------------------------------------------------------------------------------------------------83.Can you access private data members of a class from out side the class? Ans: Yes. This program shows how. #include class emp private : int i ; public : emp( ) { i = 10 ; } } ; void main( ) emp *p = new emp ; int *pi = (int*) p ; cout << *pi ; *pi = 20 ; cout << *pi ; } The pointer to the class is typecasted in an integer pointer. With the help of this pointer private data member 'i' is accessed in main( ).-------------------------------------------------------------------------------------------------84.Why creating array of references is not possible?
Ans: The array name always refers or points to the zeroeth element. If array is of references then the array name would point to the zeroeth element which happens to be a reference. Creating pointer to a reference is not valid. So, creating array of references too is not possible.
85.How do I call a virtual function of a class using a pointer to a function ? Ans : #include class Cvirtual { public : virtual float vfun( ) { cout << "from vfun" << endl ; return 7.03f ; } } ; void main( ) { Cvirtual obj ; int **p = ( int ** ) &obj ; float ( *pf1 ) ( ) ; pf1 = ( float ( * ) ( ) ) **p ; float f = ( *pf1 ) ( ) ; cout << "return val = " << f << endl ; } In the above program class Cvirtual consists of a virtual function vfun(). In variable p we have stored the address of an object of class Cvirtual. While doing so, we have type casted the address of obj to int **, because obj holds a hidden data member called vptr, which in turn holds the address of virtual function vfun( ). In pf1, a pointer to a function, we are collecting the address of the virtual function vfun( ). Thus the value returned by vfun( ) would then get collected in f.-------------------------------------------------------------------------------------------------
86.Why an overloaded new operator defined in a class is static? Ans: An overloaded new function is by default static even if it is not declared so. This is because non-static member functions can be called through an object only. But when an overloaded new operator function gets called the object doesn't stand created. Since new operator function itself is responsible for creating the object. Hence to be able to call a function without an object, the function must be static.-------------------------------------------------------------------------------------------------87.What is a pure virtual destructor?
Ans: Like a pure virtual function we can also have a pure virtual destructor. If a base class contains a pure virtual destructor it becomes necessary for the derived classes to implement the destructor. An ordinary pure virtual function does not have a body but pure virtual destructor must have a body. This is because all the destructors in the hierarchy of inheritance are always called as a part of destruction.-------------------------------------------------------------------------------------------------88.When we are required to find offset of an element within a structure? or, how do we call the function of an outer class from a function in the inner class? (The inner class is nested in the outer class) Ans: #include class outer { int i ; float f ; public : class inner { public : infunc( ) { outer *pout ; pout = (outer*) this - ( size_t ) &( ( ( outer* ) 0 ) -> in ) ; pout -> outfunc( ) ; } } ; inner in ; outfunc( ) { cout << "in outer class's function" ; } } ; void main( ) { outer out ; out.in.infunc( ) }In the above example we are calling outer::outfunc( ) from inner::infunc(). To call outfunc( ) we need a pointer to the outer class. To get the pointer we have subtracted offset of the inner class's object (base address of outer class's object - address of inner class's object) from address of inner class's object. 89.
void f ( float n, int i = 10 ) ; void f ( float a ) ; void main( ) { f ( 12.6 ) ; } void f ( float n, int i )
{ } void f ( float n ) { } The above program results in an error (ambiguous call) since without the default argument the two functions have arguments that are matching in number, order and type.-------------------------------------------------------------------------------------------------90.Some programs need to exercise precise control over the memory areas where data is placed. For example, suppose we wish to read the contents of the boot sector into a structure. For this the byte arrangement of thestructure elements must match the arrangement of various fields in the boot sector of the disk.
The #pragma pack directives offer a way to fulfill this requirement. The #pragma pack directive specifies packing alignment for structure and union members. The #pragma takes effect at the first structure or union declaration after the #pragma is seen. Consider the following structure: #pragma pack (1) struct emp { int a ; float s ; char ch ; } ; #pragma pack( )Here, #pragma pack ( 1 ) lets each structure element to begin on a 1-byte boundary. Hence the size of the structure will be 9. (int - 4, float - 4, char - 1). If we use #pragma pack ( 2 ) each structure element can begin on a 2-byte boundary. Hence the size of the structure will be 10. (int - 4, float - 4, char - 2).-------------------------------------------------------------------------------------------------91.How to restrict a friend class's access to the private data members?
Ans: If we declare a class as a friend of our class the friend class can access the private data members of our class. However, if we want we can restrict this access to some selective functions of the class. Following program shows how to achieve this: #include class X { public : void print ( class Z &z ) ;
} ; class Z { private : int i ; public : Z ( int ii ) { i = ii ; } friend X::print ( class Z &z ) ; } ; void X::print ( Z &z1 ) { cout << z1.i ; } main( ) { Z z ( 10 ) ; X x ; x.print ( 10 ) ; } In the above program only the X::print( ) function can access the private data members of class Z.-------------------------------------------------------------------------------------------------92.
What is name mangling? Ans: C++ enables you to assign the same function name to more than one functions but with different parameter types. This feature is called function overloading. But when we give several functions the same name, how does the compiler decide which particular function is to be called? C++ solves this problem by applying a process called name mangling. Name mangling applies a decorated name to the function. The mangled name includes tokens that identify the functions' return type and the types of its arguments. class test { public : void fun ( int a, char b ) ; void fun ( char *c, float y ) ; } ; void main( ) { test s1 ; s1.fun ( 65, 'A' ) ; s1.fun ( "Anil", 5.5f ) ; }At the time of resolving the calls to fun( ) function the linker would not be able to find the definition of the overloaded function fun( ) and it would report an error. If you look at these errors you will see the mangled names like, (?
fun@test@@QAEXJJ@Z) and (?fun@test@@QAEXMM@Z). Note that different compilers may use different name mangling schemes. 93.How would you call a C function from C++ code? Ans: Using extern "C".The function prototype must be preceded by extern "C". More than one C functions can be grouped inside braces as shown below: extern "C" { void f( ) ; void f1( ) ; } // In cfunc.c #include void f( ) { printf ( "in f( )" ) ; } // In func.cpp #include extern "C" void f( ) ; void main( ) { f( ) ; } Ensure that both .c and .cpp files are in the same project. -------------------------------------------------------------------------------------------------
94.How to restrict the number of floating-point digits displayed ? Ans: When we display floating-point values, we can use the setprecision manipulator to specify the desired number of digits to the right of the decimal point. For example, cout << setprecision ( 3 ) << 12.34678 ; This statement would give the output as 12.347.-------------------------------------------------------------------------------------------------95.What is a wild pointer ? Ans: A wild pointer is the one that points to a garbage value. For example, an uninitialized pointer that contains garbage value or a pointer that refers to something that no longer exists.-------------------------------------------------------------------------------------------------
96.
How friend function helps to increase the versatility of overloaded operators?
Ans: Consider the following statement, s2 = s1 * 2 ;where, s1 and s2 are objects of sample class. This statement would work if the overloaded operator * ( sample s ) or conversion function is provided in the class. Internally this statement would get converted to, s2 = s1.operator * ( 2 ) ;
The function materializes because it is called with an object s1. The this pointer of s1 would get passed implicitly. To collect 2 in s, first the compiler would call the one-argument constructor, then it would build anameless object, which then would get collected in s. However, if we write the above statement as, s2 = 2 * s1 ;then it won't compile. This is because the call now would get treated as, s2 = 2.operator * ( s1 ) ;and 2 is not an object. The friend function helps to get rid of such a situation. This is shown in the following program. #include
class sample { private : int i ; public : sample ( int ii = 0 ) { i = ii ; }
Here the operator *( ) function takes two parameters. This is because the operator function is no longer a member function of the class. It is a friend of the class sample. Thus the statement s2 = s1 * 2 ; would not take the form s2.operator * ( 2 ). This example shows that using friend permits the overloaded operators to be more versatile. 97.
What is a const_cast?
Ans: The const_cast is used to convert a const to a non-const. This is shown in the following program. #include
void main( ) { const int a = 0 ;
int *ptr = ( int * ) &a ; // one way ptr = const_cast ( &a ) ; // better way }
Here, the address of the const variable a is assigned to the pointer to a non-const variable. The const_cast is also used when we want to change the data members of a class inside the const member functions. The following code snippet shows how to do this. class sample { private : int data ; public : void fun( ) const { ( const_cast ( this ) ) -> data = 70 ; } } ;-------------------------------------------------------------------------------------------------98.Using a smart pointer we can make an object appear like a pointer.
If a class overloads the operator -> then any object of that class can appear like a pointer when the operator -> ( ) is called. The following program illustrates this. #include
class test { public : void fun( ) { cout << "fun of smart pointer" ; }
} ;
class smartpointer { test t ; public : test* operator ->( ) { return &t ; } } ;
void main( ) { smartpointer sp ; sp -> fun( ) ; }The beauty of overloading operator -> is that even though sp is an object we can make it work like a pointer. The operator -> ( ) returns the address of the object of the type test. Using this address of the test object the function fun( ) of the class test gets called. Thus even though fun( ) is not a member of smartpointer class we can still call it using sp. -------------------------------------------------------------------------------------------------99.Can we apply delete on this pointer inside a member function?
Ans : Yes! If the member function of a class is called using a pointer to an object, which is allocated dynamically, the object would get deleted. But if the member function is called using the object, which is allocated statically, then a runtime error would occur. This is because we cannot call delete on statically allocated objects. This is illustrated in the following example. class sample { private : int i ; public : void fun( ) { delete this ; } } ;
void main( ) { sample *s = new sample ; s -> fun( ) ; // no error
sample s1 ; s1.fun( ) ; // would throw a runtime error } 100.
Why can't data members of a class be initialized at the time of declaration as given in the following code? class emp { private : int j = 10 ; } ;Ans: Memory for data members of a class is allocated only when object of that class is created. One cannot store data in a memory location, which does not exist at all. Therefore initialization at the time of declarationis not possible.-------------------------------------------------------------------------------------------------101.
Why in a copy constructor an object is collected in a reference to object as shown below? #include class emp { public : emp( ) { } emp ( emp& ) { cout << "copy" ; } } ; void main( ) { emp e ; emp e1 = e ; }Ans: A copy constructor is called when an object is created and initialised at the same time. It is also called when object is passed to a function. So, If we pass the object to copy constructor copy constructor would get called recursively. Thus it will stuck up in an infinite loop.-------------------------------------------------------------------------------------------------102.
What is Early Binding and Dynamic Binding?Ans: The term binding refers to the connection between a function call and the actual code executed as a result of the call. Early Binding: If which function is to be called is known at the compile-time it is known as static or early binding. Dynamic Binding: If which function is to be called is decided at run time it is called as late or dynamic binding. Dynamic binding is so called because the actual function called at run-time depends on the contents of the pointer. For example, call to virtual functions, call to functions to be linked from dlls use late binding.-------------------------------------------------------------------------------------------------103.
When can we use the function ostrstream::freeze( )?
Ans: While outputting data to memory in the in-memory formatting we need to create an object of the class ostrstream. The constructor of ostrstream receives the address of the buffer but if we want that the ostrstreamobject should do its own memory management then we need to create an ostrstream object with no constructor arguments as: ostrstream s ;Now s will do its own memory management. We can stuff as many bytes into it as we want. If it falls short of memory, it will allocate more memory. If it cannot, it may even move the block of memory. When the object goes out of scope, the heap storage is automatically released. This is a more flexible approach if we do not know how much space we are going to need. If we want the physical address of the memory used by s we can obtain it by calling the str( ) member function: char* p = s.str( ) ;Once str( ) has been called then the block of memory allocated by ostrstream cannot be moved. This is logical. It can't move the block since we are now expecting it to be at a particular location. In such a case wesay that ostrstream has freezed itself. Once frozen we can't add any more characters to it. Adding characters to a frozen ostrstream results in undefined behavior. In addition, the ostrstream is no longer responsible for cleaning up the storage. You took over that responsibility when you asked for the char * with str( ). We can clean the storage in two ways: Using the delete operator as shown below: ostrstream s ; char *p ; p = s.str( ) ; delete p ;By unfreezing the ostrstream. You do this by calling freeze( ), with an argument 1. During freezing it is called with the default argument of 0.
java#############3FAQ In Core Java1.what is a transient variable?A transient variable is a variable that may not be serialized.
2.which containers use a border Layout as their default layout?The window, Frame and Dialog classes use a border layout as their default layout.
3.Why do threads block on I/O?Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed.
4. How are Observer and Observable used?Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
5. What is synchronization and why is it important?With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.
6. Can a lock be acquired on a class?Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object..
7. What's new with the stop(), suspend() and resume() methods in JDK 1.2?The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
8. Is null a keyword?The null value is not a keyword.
9. What is the preferred size of a component?The preferred size of a component is the minimum component size that will allow the component to display normally.
10. What method is used to specify a container's layout?The setLayout() method is used to specify a container's layout.
11. Which containers use a FlowLayout as their default layout?The Panel and Applet classes use the FlowLayout as their default layout.
12. What state does a thread enter when it terminates its processing?When a thread terminates its processing, it enters the dead state.13. What is the Collections API?The Collections API is a set of classes and interfaces that support operations on collections of objects.
14. Which characters may be used as the second character of an identifier,but not as the first character of an identifier?The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
15. What is the List interface?
The List interface provides support for ordered collections of objects.
16. How does Java handle integer overflows and underflows?It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
17. What is the Vector class?The Vector class provides the capability to implement a growable array of objects
18. What modifiers may be used with an inner class that is a member of an outer class?A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
19. What is an Iterator interface?The Iterator interface is used to step through the elements of a Collection.
20. What is the difference between the >> and >>> operators?The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.
21. Which method of the Component class is used to set the position andsize of a component?setBounds()
22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
23What is the difference between yielding and sleeping?When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.24. Which java.util classes and interfaces support event handling?The EventObject class and the EventListener interface support event processing.
25. Is sizeof a keyword?The sizeof operator is not a keyword.
26. What are wrapped classes?Wrapped classes are classes that allow primitive types to be accessed as objects.
27. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
28. What restrictions are placed on the location of a package statementwithin a source code file?A package statement must appear as the first line in a source code file (excluding blank lines and comments).
29. Can an object's finalize() method be invoked while it is reachable?An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.
30. What is the immediate superclass of the Applet class?Panel
31. What is the difference between preemptive scheduling and time slicing?Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority andother factors.
32. Name three Component subclasses that support painting.The Canvas, Frame, Panel, and Applet classes support painting.
33. What value does readLine() return when it has reached the end of a file?The readLine() method returns null when it has reached the end of a file.
34. What is the immediate superclass of the Dialog class?Window
35. What is clipping?Clipping is the process of confining paint operations to a limited area or shape.
36. What is a native method?A native method is a method that is implemented in a language other than Java.
37. Can a for statement loop indefinitely?Yes, a for statement can loop indefinitely. For example, consider the following:for(;;) ;
38. What are order of precedence and associativity, and how are they used?Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left
39. When a thread blocks on I/O, what state does it enter?A thread enters the waiting state when it blocks on I/O.
40. To what value is a variable of the String type automatically initialized?The default value of an String type is null.
41. What is the catch or declare rule for method declarations?If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
42. What is the difference between a MenuItem and a CheckboxMenuItem?The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
43. What is a task's priority and how is it used in scheduling?A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.
44. What class is the top of the AWT event hierarchy?The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy.
45. When a thread is created and started, what is its initial state?A thread is in the ready state after it has been created and started.
46. Can an anonymous class be declared as implementing an interface and extending a class?An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
47. What is the range of the short type?The range of the short type is -(2^15) to 2^15 - 1.
48. What is the range of the char type?The range of the char type is 0 to 2^16 - 1.
49. In which package are most of the AWT events that support the event-delegationmodel defined?Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.
50. What is the immediate superclass of Menu?
MenuItem
51. What is the purpose of finalization?The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
52. Which class is the immediate superclass of the MenuComponent class.Object
53. What invokes a thread's run() method?After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
54. What is the difference between the Boolean & operator and the && operator?If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
55. Name three subclasses of the Component class.Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent
56. What is the GregorianCalendar class?The GregorianCalendar provides support for traditional Western calendars.
57. Which Container method is used to cause a container to be laid out and redisplayed?validate()
58. What is the purpose of the Runtime class?The purpose of the Runtime class is to provide access to the Java runtime system.
59. How many times may an object's finalize() method be invoked by thegarbage collector?An object's finalize() method may only be invoked once by the garbage collector.
60. What is the purpose of the finally clause of a try-catch-finally statement?The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.
61. What is the argument type of a program's main() method?
A program's main() method takes an argument of the String[] type.
62. Which Java operator is right associative?The = operator is right associative.
63. What is the Locale class?The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.
64. Can a double value be cast to a byte?Yes, a double value can be cast to a byte.
65. What is the difference between a break statement and a continue statement?A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.
66. What must a class do to implement an interface?It must provide all of the methods in the interface and identify the interface in its implements clause.
67. What method is invoked to cause an object to begin executing as a separate thread?The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.
68. Name two subclasses of the TextComponent class.TextField and TextArea
69. What is the advantage of the event-delegation model over the earlier event-inheritance model?The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance model.70. Which containers may have a MenuBar?Frame
71. How are commas used in the intialization and iteration parts of a for statement?Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.
72. What is the purpose of the wait(), notify(), and notifyAll() methods?The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared
resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods..
73. What is an abstract method?An abstract method is a method whose implementation is deferred to a subclass.
74. How are Java source code files named?A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the .java extension.
75. What is the relationship between the Canvas class and the Graphics class?A Canvas object provides access to a Graphics object via its paint() method.
76. What are the high-level thread states?The high-level thread states are ready, running, waiting, and dead.
77. What value does read() return when it has reached the end of a file?The read() method returns -1 when it has reached the end of a file.
78. Can a Byte object be cast to a double value?No, an object cannot be cast to a primitive value.
79. What is the difference between a static and a non-static inner class?A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.80. What is the difference between the String and StringBuffer classes?String objects are constants. StringBuffer objects are not.
81. If a variable is declared as private, where may the variable be accessed?A private variable may only be accessed within the class in which it is declared.
82. What is an object's lock and which object's have locks?An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
83. What is the Dictionary class?The Dictionary class provides the capability to store key-value pairs.
84. How are the elements of a BorderLayout organized?The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container.
85. What is the % operator?It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
86. When can an object reference be cast to an interface reference?An object reference be cast to an interface reference when the object implements the referenced interface.
87. What is the difference between a Window and a Frame?The Frame class extends Window to define a main application window that can have a menu bar.
88. Which class is extended by all other classes?The Object class is extended by all other classes.
89. Can an object be garbage collected while it is still reachable?A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected..
90. Is the ternary operator written x : y ? z or x ? y : z ?It is written x ? y : z.
91. What is the difference between the Font and FontMetrics classes?The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
92. How is rounding performed under integer division?The fractional part of the result is truncated. This is known as rounding toward zero.
93. What happens when a thread cannot acquire a lock on an object?If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
94. What is the difference between the Reader/Writer class hierarchy and theInputStream/OutputStream class hierarchy?The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
95. What classes of exceptions may be caught by a catch clause?A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
96. If a class is declared without any access modifiers, where may the class be accessed?A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
97. What is the SimpleTimeZone class?The SimpleTimeZone class provides support for a Gregorian calendar.
98. What is the Map interface?The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
99. Does a class inherit the constructors of its superclass?A class does not inherit constructors from any of its superclasses.
100. For which statements does it make sense to use a label?The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement.
101. What is the purpose of the System class?The purpose of the System class is to provide access to system resources.
102. Which TextComponent method is used to set a TextComponent to the read-only state?setEditable()
103. How are the elements of a CardLayout organized?The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.
104. Is &&= a valid Java operator?No, it is not.
105. Name the eight primitive Java types.The eight primitive types are byte, char, short, int, long, float, double, and boolean.
106. Which class should you use to obtain design information about an object?The Class class is used to obtain information about an object's design.
107. What is the relationship between clipping and repainting?
When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.
108. Is "abc" a primitive value?The String literal "abc" is not a primitive value. It is a String object.
109. What is the relationship between an event-listener interface and anevent-adapter class?An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface.
110. What restrictions are placed on the values of each case of a switch statement?During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.
111. What modifiers may be used with an interface declaration?An interface may be declared as public or abstract.
112. Is a class a subclass of itself?A class is a subclass of itself.
113. What is the highest-level event class of the event-delegation model?The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
114. What event results from the clicking of a button?The ActionEvent event is generated as the result of the clicking of a button.
115. How can a GUI component handle its own events?A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.116. What is the difference between a while statement and a do statement?A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.
117. How are the elements of a GridBagLayout organized?The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
118. What advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accomodate platform-specific differences among windowing systems.
119. What is the Collection interface?The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
120. What modifiers can be used with a local inner class?A local inner class may be final or abstract.
121. What is the difference between static and non-static variables?A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
122. What is the difference between the paint() and repaint() methods?The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
123. What is the purpose of the File class?The File class is used to create objects that provide access to the files and directories of a local file system.
124. Can an exception be rethrown?Yes, an exception can be rethrown.125. Which Math method is used to calculate the absolute value of a number?The abs() method is used to calculate absolute values.
126. How does multithreading take place on a computer with a single CPU?The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
127. When does the compiler supply a default constructor for a class?The compiler supplies a default constructor for a class if no other constructors are provided.
128. When is the finally clause of a try-catch-finally statement executed?The finally clause of the try-catch-finally statement is always executed unless the thread of execution terminates or an exception occurs within the execution of the finally clause.
129. Which class is the immediate superclass of the Container class?Component
130. If a method is declared as protected, where may the method be accessed?A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
131. How can the Checkbox class be used to create a radio button?By associating Checkbox objects with a CheckboxGroup.
132. Which non-Unicode letter characters may be used as the first characterof an identifier?The non-Unicode letter characters $ and _ may appear as the first character of an identifier
133. What restrictions are placed on method overloading?Two methods may not have the same name and argument list but different return types.
134. What happens when you invoke a thread's interrupt method while it issleeping or waiting?When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.
135. What is casting?There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
136. What is the return type of a program's main() method?A program's main() method has a void return type.
137. Name four Container classes.Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane
138. What is the difference between a Choice and a List?A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.
139. What class of exceptions are generated by the Java run-time system?The Java runtime system generates RuntimeException and Error exceptions.
140. What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
141. What is the difference between a field variable and a local variable?A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.
142. Under what conditions is an object's finalize() method invoked by the garbage collector?The garbage collector invokes an object's finalize() method when it detects that the object has become unreachable.
143. How are this() and super() used with constructors?this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
144. What is the relationship between a method's throws clause and the exceptionsthat can be thrown during the method's execution?A method's throws clause must declare any checked exceptions that are not caught within the body of the method.
145. What is the difference between the JDK 1.02 event model and the event-delegationmodel introduced with JDK 1.1?The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model, components are required to handle their own events. If they do not handle a particular event, the event is inherited by (or bubbled up to) the component's container. The container then either handles the event or it is bubbled up to its container and so on, until the highest-level container has been tried..In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces. The event-delegation model is more efficient than the event-inheritance model because it eliminates the processing required to support the bubbling of unhandled events.146. How is it possible for two String objects with identical values not to be equalunder the == operator?The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.
147. Why are the methods of the Math class static?So they can be invoked as if they are a mathematical code library.
148. What Checkbox method allows you to tell if a Checkbox is checked?getState()
149. What state is a thread in when it is executing?An executing thread is in the running state.
150. What are the legal operands of the instanceof operator?The left operand is an object reference or null value and the right operand is a class, interface, or array type.
151. How are the elements of a GridLayout organized?The elements of a GridBad layout are of equal size and are laid out using the squares of a grid.
152. What an I/O filter?An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
153. If an object is garbage collected, can it become reachable again?Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.
154. What is the Set interface?The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
155. What classes of exceptions may be thrown by a throw statement?A throw statement may throw any expression that may be assigned to the Throwable type.156. What are E and PI?E is the base of the natural logarithm and PI is mathematical value pi.
157. Are true and false keywords?The values true and false are not keywords.
158. What is a void return type?A void return type indicates that a method does not return a value.
159. What is the purpose of the enableEvents() method?The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
160. What is the difference between the File and RandomAccessFile classes?The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
161. What happens when you add a double value to a String?The result is a String object.
162. What is your platform's default character encoding?
If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1..
163. Which package is always imported by default?The java.lang package is always imported by default.
164. What interface must an object implement before it can be written to astream as an object?An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
165. How are this and super used?this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.
166. What is the purpose of garbage collection?The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.167. What is a compilation unit?A compilation unit is a Java source code file.
168. What interface is extended by AWT event listeners?All AWT event listeners extend the java.util.EventListener interface.
169. What restrictions are placed on method overriding?Overridden methods must have the same name, argument list, and return type.The overriding method may not limit the access of the method it overrides.The overriding method may not throw any exceptions that may not be thrownby the overridden method.
170. How can a dead thread be restarted?A dead thread cannot be restarted.
171. What happens if an exception is not caught?An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.
172. What is a layout manager?A layout manager is an object that is used to organize components in a container.
173. Which arithmetic operations can result in the throwing of an ArithmeticException?Integer / and % can result in the throwing of an ArithmeticException.
174. What are three ways in which a thread can enter the waiting state?
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
175. Can an abstract class be final?An abstract class may not be declared as final.
176. What is the ResourceBundle class?The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
177. What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement?The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination.
178. What is numeric promotion?Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.
179. What is the difference between a Scrollbar and a ScrollPane?A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
180. What is the difference between a public and a non-public class?A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.
181. To what value is a variable of the boolean type automatically initialized?The default value of the boolean type is false.
182. Can try statements be nested?Try statements may be tested.
183. What is the difference between the prefix and postfix forms of the ++ operator?The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.
184. What is the purpose of a statement block?
A statement block is used to organize a sequence of statements as a single statement group.
185. What is a Java package and how is it used?A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
186. What modifiers may be used with a top-level class?A top-level class may be public, abstract, or final.
187. What are the Object and Class classes used for?The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program..188. How does a try statement determine which catch clause should be used to handle an exception?When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.
189. Can an unreachable object become reachable again?An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.
190. When is an object subject to garbage collection?An object is subject to garbage collection when it becomes unreachable to the program in which it is used.
191. What method must be implemented by all threads?All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.
192. What methods are used to get and set the text label displayed by a Button object?getLabel() and setLabel()
193. Which Component subclass is used for drawing and painting?Canvas
194. What are synchronized methods and synchronized statements?Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
195. What are the two basic ways in which classes that can be run as threads may be defined?A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.
196. What are the problems faced by Java programmers who don't use layout managers?Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.
197. What is the difference between an if statement and a switch statement?The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.
198. What happens when you add a double value to a String?The result is a String object.
199. What is the List interface?The List interface provides support for ordered collections of objects.
************************************FAQ In Object Oriented Concepts*********************************· How do you write a program which produces its own source code as its output?· How can I find the day of the week given the date?· Why doesn't C have nested functions?· What is the most efficient way to count the number of bits which are set in a value?· How can I convert integers to binary or hexadecimal?· How can I call a function, given its name as a string?· How do I access command-line arguments?· How can I return multiple values from a function?· How can I invoke another program from within a C program?· How can I access memory located at a certain address?· How can I allocate arrays or structures bigger than 64K?· How can I find out how much memory is available?· How can I read a directory in a C program?· How can I increase the allowable number of simultaneously open files?· What's wrong with the call "fopen("c:\newdir\file.dat", "r")"?· What is the output of printf("%d")· What will happen if I say delete this· Difference between "C structure" and "C++ structure".· Diffrence between a "assignment operator" and a "copy constructor"
· What is the difference between "overloading" and "overridding"?· Explain the need for "Virtual Destructor".· Can we have "Virtual Constructors"?· What are the different types of polymorphism?· What are Virtual Functions? How to implement virtual functions in "C"· What are the different types of Storage classes?· What is Namespace?· What are the types of STL containers?.· Difference between "vector" and "array"?· How to write a program such that it will delete itself after exectution?· Can we generate a C++ source code from the binary file?· What are inline functions?· Talk sometiming about profiling?· How many lines of code you have written for a single program?· What is "strstream" ?· How to write Multithreaded applications using C++?· Explain "passing by value", "passing by pointer" and "passing by reference"· Write any small program that will compile in "C" but not in "C++"· Have you heard of "mutable" keyword?· What is a "RTTI"?
· Is there something that I can do in C and not in C++?· Why preincrement operator is faster than postincrement?· What is the difference between "calloc" and "malloc"?· What will happen if I allocate memory using "new" and free it using "free" or allocate sing "calloc" and free it using "delete"?· What is Memory Alignment?· Explain working of printf.· Difference between "printf" and "sprintf".· What is "map" in STL?· When shall I use Multiple Inheritance?· What are the techniques you use for debugging?· How to reduce a final size of executable?· Give 2 examples of a code optimization.· What is inheritance?· Difference between Composition and Aggregation.· Difference: Sequence Diagrams, Collaboration Diagrams.· Difference: 'uses', 'extends', 'includes'· What shall I go for Package Diagram?· What is Polymorphism?· Is class an Object? Is object a class?· Comment: C++ "includes" behavior and java "imports"· What do you mean by "Realization"?· What is a Presistent, Transient Object?· What is the use of Operator Overloading?· Does UML guarantee project success?· Difference: Activity Diagram and Sequence Diagram.· What is association?· How to resolve many to many relationship?· How do you represent static members and abstract classes in Class Diagram?
· What does static variable mean?· What is a pointer?· What is a structure?· What are the differences between structures and arrays?· In header files whether functions are declared or defined?· What are the differences between malloc() and calloc()?· What are macros? what are its advantages and disadvantages?· Difference between pass by reference and pass by value?· What is static identifier?· Where are the auto variables stored? · Where does global, static, local, register variables, free memory and C Program instructions get stored?· Difference between arrays and linked list?· What are enumerations?· Describe about storage allocation and scope of global, extern, static, local and register variables?· What are register variables? What are the advantage of using register variables?· What is the use of typedef?· Can we specify variable field width in a scanf() format string? If possible how?· Out of fgets() and gets() which function is safe to use and why?· Difference between strdup and strcpy?· What is recursion?· Differentiate between a for loop and a while loop? What are it uses?· What are the different storage classes in C?· Write down the equivalent pointer expression for referring the same element a[i][j][k][l]?· What is difference between Structure and Unions?· What the advantages of using Unions?· What are the advantages of using pointers in a program?· What is the difference between Strings and Arrays?· In a header file whether functions are declared or defined?· What is a far pointer? where we use it?· How will you declare an array of three function pointers where each function receives two ints and returns a float?· what is a NULL Pointer? Whether it is same as an uninitialized pointer?· What is a NULL Macro? What is the difference between a NULL Pointer and a NULL Macro?· What does the error 'Null Pointer Assignment' mean and what causes this error?· What is near, far and huge pointers? How many bytes are occupied by them?· How would you obtain segment and offset addresses from a far address of a memory location?· Are the expressions arr and &arr same for an array of integers?· Does mentioning the array name gives the base address in all the contexts?· Explain one method to process an entire string as one unit?· What is the similarity between a Structure, Union and enumeration?· Can a Structure contain a Pointer to itself?
· How can we check whether the contents of two structure variables are same or not?· How are Structure passing and returning implemented by the complier?· How can we read/write Structures from/to data files?· What is the difference between an enumeration and a set of pre-processor # defines?· what do the 'c' and 'v' in argc and argv stand for?· Are the variables argc and argv are local to main? What is the maximum combined length of command line arguments including the space between adjacent arguments?· If we want that any wildcard characters in the command line arguments should be appropriately expanded, are we required to make any special provision? If yes, which?· Does there exist any way to make the command line arguments available to other functions without passing them as arguments to the function?· What are bit fields? What is the use of bit fields in a Structure declaration?· To which numbering system can the binary number 1101100100111100 be easily converted to?· Which bit wise operator is suitable for checking whether a particular bit is on or off?· Which bit wise operator is suitable for turning off a particular bit in a number?· Which bit wise operator is suitable for putting on a particular bit in a number?· Which bit wise operator is suitable for checking whether a particular bit is on or off?· which one is equivalent to multiplying by 2:Left shifting a number by 1 or Left shifting an unsigned int or char by 1?· Write a program to compare two strings without using the strcmp() function.· Write a program to concatenate two strings.· Write a program to interchange 2 variables without using the third one.· Write programs for String Reversal & Palindrome check· Write a program to find the Factorial of a number· Write a program to generate the Fibinocci Series· Write a program which employs Recursion· Write a program which uses Command Line Arguments· Write a program which uses functions like strcmp(), strcpy()? etc· What are the advantages of using typedef in a program?· How would you dynamically allocate a one-dimensional and two-dimensional array of integers?· How can you increase the size of a dynamically allocated array?· How can you increase the size of a statically allocated array?· When reallocating memory if any other pointers point into the same piece of memory do you have to readjust these other pointers or do they get readjusted automatically?· Which function should be used to free the memory allocated by calloc()?· How much maximum can you allocate in a single call to malloc()?· Can you dynamically allocate arrays in expanded memory?
· What is object file? How can you access object file? Which header file should you include if you are to develop a function which can accept variable number of arguments?· Can you write a function similar to printf()?· How can a called function determine the number of arguments that have been passed to it?· Can there be at least some solution to determine the number of arguments passed to a variable argument list function?· How do you declare the following:· An array of three pointers to chars· An array of three char pointers· A pointer to array of three chars· A pointer to function which receives an int pointer and returns a float pointer· A pointer to a function which receives nothing and returns nothing· What do the functions atoi(), itoa() and gcvt() do?· Does there exist any other function which can be used to convert an integer or a float to a string?· How would you use qsort() function to sort an array of structures?· How would you use qsort() function to sort the name stored in an array of pointers to string?· How would you use bsearch() function to search a name stored in array of pointers to string?· How would you use the functions sin(), pow(), sqrt()?· How would you use the functions memcpy(), memset(), memmove()?· How would you use the functions fseek(), freed(), fwrite() and ftell()?· How would you obtain the current time and difference between two times?· How would you use the functions randomize() and random()?· How would you implement a substr() function that extracts a sub string from a given string?· What is the difference between the functions rand(), random(), srand() and randomize()?· What is the difference between the functions memmove() and memcpy()?· How do you print a string on the printer?· Can you use the function fprintf() to display the output on the screen?· What is an object?· What is the difference between an object and a class?· What is the difference between class and structure?· What is public, protected, private?· What are virtual functions? · What is friend function?· What is a scope resolution operator?· What do you mean by inheritance?· What is abstraction?· What is polymorphism? Explain with an example.· What is encapsulation?· What do you mean by binding of data and functions?· What is function overloading and operator overloading?· What is virtual class and friend class?
· What do you mean by inline function?· What do you mean by public, private, protected and friendly?· When is an object created and what is its lifetime?· What do you mean by multiple inheritance and multilevel inheritance? Differentiate between them.· Difference between realloc() and free?· What is a template?· What are the main differences between procedure oriented languages and object oriented languages?· What is R T T I ?· What are generic functions and generic classes?· What is namespace?· What is the difference between pass by reference and pass by value?· Why do we use virtual functions?· What do you mean by pure virtual functions?· What are virtual classes?· Does c++ support multilevel and multiple inheritance?· What are the advantages of inheritance?· When is a memory allocated to a class?· What is the difference between declaration and definition?· What is virtual constructors/destructors?· In c++ there is only virtual destructors, no constructors. Why?· What is late bound function call and early bound function call? Differentiate.· How is exception handling carried out in c++?· When will a constructor executed?· What is Dynamic Polymorphism?· Write a macro for swapping integers. ***************************************************************************************************
FAQ In Testing Tools
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Software QA and Testing Frequently-Asked-Questions
1.What is 'Software Quality Assurance'?
Software QA involves the entire software development PROCESS - monitoring and improving the process, making sure that any agreed- upon standards and procedures are followed, and ensuring that problems are found and dealt with. It is oriented to 'prevention'.
2.What is 'Software Testing'?
Testing involves operation of a system or application under controlled conditions and evaluating the results (eg, 'if the user is in interface A of the application while using hardware B, and does C, then D should happen'). The controlled conditions should include both normal and abnormal conditions. Testing should intentionally attempt to make
things go wrong to determine if things happen when they shouldn't or things don't happen when they should. It is oriented to 'detection'.
3.What are some recent major computer system failures caused by software bugs?
In April of 2003 it was announced that the largest student loan company in the U.S. made a software error in calculating the monthly payments on 800,000 loans. Although borrowers were to be notified of an increase in their required payments, the company will still reportedly lose $8 million in interest. The error was uncovered when borrowers began reporting inconsistencies in their bills.
News reports in February of 2003 revealed that the U.S. Treasury Department mailed 50,000 Social Security checks without any beneficiary names. A spokesperson indicated that the missing names were due to an error in a software change. Replacement checks were subsequently mailed out with the problem corrected, and recipients were then able to cash their Social Security checks.
In March of 2002 it was reported that software bugs in Britain's national tax system resulted in more than 100,000erroneous tax overcharges. The problem was partly attibuted to the difficulty of testing the integration of multiple systems.
A newspaper columnist reported in July 2001 that a serious flaw was found in off-the-shelf software that had long been used in systems for tracking certain U.S. nuclear materials. The same software had been recently donated to another country to be used in tracking their own nuclear materials, and it was not until scientists in that country discovered the problem, and shared the information, that U.S. officials became aware of the problems. According to newspaper stories in mid-2001, a major systems development contractor was fired and sued over problems with a large retirement plan management system. According to the reports, the client claimed that system deliveries were late, the software had excessive defects, and it caused other systems to crash.
In January of 2001 newspapers reported that a major European railroad was hit by the aftereffects of the Y2K bug. The company found that many of their newer trains would not run due to their inability to recognize the date '31/12/2000'; the trains were started by altering the control system's date settings.News reports in September of 2000 told of a software vendor settling a lawsuit with a large mortgage lender; the vendor had reportedly delivered an online mortgage processing system that did not meet specifications, was delivered late, and didn't work.
In early 2000, major problems were reported with a new computer system in a large suburban U.S. public school district with 100,000+ students; problems included 10,000 erroneous report cards and students left stranded by failed
class registration systems; the district's CIO was fired. The school district decided to reinstate it's original 25-year old system for at least a year until the bugs were worked out of the new system by the software vendors.
In October of 1999 the $125 million NASA Mars Climate Orbiter spacecraft was believed to be lost in space due to a simple data conversion error. It was determined that spacecraft software used certain data in English units that should have been in metric units. Among other tasks, the orbiter was to serve as a communications relay for the Mars Polar Lander mission, which failed for unknown reasons in December 1999. Several investigating panels were convened to determine the process failures that allowed the error to go undetected.
Bugs in software supporting a large commercial high-speed data network affected 70,000 business customers over a period of 8 days in August of 1999. Among those affected was the electronic trading system of the largest U.S. futures exchange, which was shut down for most of a week as a result of the outages.
In April of 1999 a software bug caused the failure of a $1.2 billion military satellite launch, the costliest unmanned accident in the history of Cape Canaveral launches. The failure was the latest in a string of launch failures, triggering a complete military and industry review of U.S. space launch programs, including software integration and testing processes. Congressional oversight hearings were requested.
A small town in Illinois received an unusually large monthly electric bill of $7 million in March of 1999. This was about700 times larger than its normal bill. It turned out to be due to bugs in new software that had been purchased by the local power company to deal with Y2K software issues.
