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Chapter 11
Structured Types,
Data Abstraction and Classes
Dale/Weems/Headington
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Chapter 11 Topics Meaning of a Structured Data Type Declaring and Using a struct Data Type C++ union Data Type Meaning of an Abstract Data Type Declaring and Using a class Data Type Using Separate Specification and
Implementation Files Invoking class Member Functions in Client
Code C++ class Constructors
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C++ Data TypesC++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
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Structs
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Structured Data Type
A structured data type is a type in which each value is a collection of component items.
the entire collection has a single name
each component can be accessed individually
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C++ Structured Type
often we have related information of various types that we’d like to store together for convenient access under the same identifier, for example . . .
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thisAnimal
5000
.id 2037581
.name “giant panda”
.genus “Ailuropoda”
.species “melanoluka”
.country “China”
.age 18
.weight 234.6
.health Good
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anotherAnimal
6000
.id 5281003
.name “llama”
.genus “Lama”
.species “peruana”
.country “Peru”
.age 7
.weight 278.5
.health Excellent
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struct AnimalType
enum HealthType { Poor, Fair, Good, Excellent } ;
struct AnimalType // declares a struct data type{ // does not allocate memory
int id ;string name ;string genus ;string species ; struct members string country ; int age ; float weight ;
} ;
AnimalType thisAnimal ; // declare variables of AnimalType
AnimalType anotherAnimal ;
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struct type Declaration
SYNTAX struct TypeName // does not allocate memory {
MemberList } ;
MemberList SYNTAX
DataType MemberName ;
DataType MemberName ; . . .
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struct type Declaration
The struct declaration names a type and names the members of the struct.
It does not allocate memory for any variables of that type!
You still need to declare your struct variables.
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More about struct type declarations
If struct type declaration precedes all functions visible throughout the rest of the file (global scope).
If it is placed within a function, only that function can use it (local scope).
Common to place struct type decl. in (.h) header file#include that file.
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More about struct type declarations
Members of different struct types MAY have the same identifiers (names).
struct Student struct Instructor
{ {int id; int id;
float gpa; float salary;
} }
Non-struct variable MAY have the same identifier as a structure member.
Student s;
float gpa;
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Accessing struct Members
Dot ( period ) is the member selection operator.
After struct type declaration: struct members can be used in your program only when they are preceded by
– dot– a struct variable name
EXAMPLESAnimalType thisAnimal,
anotherAnimal;thisAnimal.weightanotherAnimal.country
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Valid operations on a struct member depend only on its type
thisAnimal.age = 18;
thisAnimal.id = 2037581;
cin >> thisAnimal.weight;
getline ( cin, thisAnimal.species );
thisAnimal.name = “giant panda”;
thisAnimal.genus[ 0 ] = toupper (thisAnimal.genus[ 0 ] ) ;
thisAnimal.age++;
struct AnimalType { long id ;
string name ;string genus ;string species; string country
int age ;
float weight ;
HealthType health ;
} ;
AnimalType thisAnimal;
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Aggregate Operations
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Aggregate Operation
is an operation on a
data structure as a whole
as opposed to an operation on an individual component of the data structure
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Aggregate struct Operations
NOT ALLOWED I/O arithmetic comparisons of entire struct variables
Operations ALLOWED on entire struct variable:
assignment to another struct variable of same type pass to a function as argument (by value or by reference)
return as value of a function
see time1.cpp time2.cpp
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Examples of aggregate struct operations
anotherAnimal = thisAnimal ; // assignment
WriteOut(thisAnimal); // value parameter
ChangeWeightAndAge(thisAnimal); // reference parameter
thisAnimal = GetAnimalData( ); // return value of function
NOW WE’LL WRITE THE 3 FUNCTIONS USED HERE . . .
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void WriteOut( /* in */ AnimalType thisAnimal)
// Prints out values of all members of thisAnimal
// Precondition: all members of thisAnimal are assigned
// Postcondition: all members have been written out{
cout << “ID # “ << thisAnimal.id << thisAnimal.name << endl ;
cout << thisAnimal.genus << thisAnimal.species << endl ;
cout << thisAnimal.country << endl ;
cout << thisAnimal.age << “ years “ << endl ;
cout << thisAnimal.weight << “ lbs. “ << endl ;
cout << “General health : “ ;
WriteWord ( thisAnimal.health ) ;}
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void ChangeAge ( /* inout */ AnimalType& thisAnimal )
// Adds 1 to age// Precondition: thisAnimal.age is assigned // Postcondition: thisAnimal.age == thisAnimal.age@entry + 1
{
thisAnimal.age++ ;
}
Passing a struct Type by Reference
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AnimalType GetAnimalData ( void )
// Obtains all information about an animal from keyboard
// Postcondition:// Function value == AnimalType members entered at kbd{
AnimalType thisAnimal ;
char response ;
do { // have user enter all members until they are correct.
.
.
} while (response != ‘Y’ ) ;
return thisAnimal ;
}
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Hierarchical Structures
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Hierarchical Structures
A struct member can be of another struct type.
This is called nested or hierarchical structures.
Hierarchical structures are useful when there is detailed info in each record.
FOR EXAMPLE . . .
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struct MachineRec
Information about each machine in a shop contains:
an idNumber,
a written description,
the purchase date,
the cost,
and a historical statistics (including failure rate, number of days down, and date of last service).
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struct DateType
{ int month ; // Assume 1 . . 12
int day ; // Assume 1 . . 31
int year ; // Assume 1900 . . 2050
};
struct StatisticsType
{ float failRate ;
DateType lastServiced ; // DateType is a struct type
int downDays ;
} ;
struct MachineRec
{ int idNumber ;
string description ;
StatisticsType history ; // StatisticsType is a struct type
DateType purchaseDate ;
float cost ;
} ;
MachineRec machine ;
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struct type variable machine
7000
.idNumber .description . history .purchaseDate .cost
.month .day .year
5719 “BULLDOZ…” 3 21 1995 78000.
.failrate .lastServiced .downdays
.02 6 25 1999 4.month .day .year
machine.history.lastServiced.year has value 1999
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Unions
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Unions in C++
DEFINITION
A union is a struct that holds only one of its members at a time during program execution.
EXAMPLE
union WeightType
{
long wtInOunces ; int wtInPounds; only one at a time
float wtInTons;
} ;
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Using Unions
union WeightType // declares a union type
{
long wtInOunces ;
int wtInPounds;
float wtInTons;
} ;
WeightType weight; // declares a union variable
weight.wtInTons = 4.83 ;
// Weight in tons is no longer needed. Reuse the memory space.
weight.wtInPounds = 35; // see Unionex.cpp
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Abstraction
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Abstraction
Is the separation of the essential qualities of an object from the details of how it works or is composed
Essential qualities <<<<>>>> details
Focuses on what, not how Like a table of contents Is necessary for managing large, complex
software projects
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Control Abstraction separates the logical properties of an action
from its implementation logical properties <<<>>> implementation
. . .
Search (list, item, length, where, found); . . .
the function call depends on the function’s specification (description), not its implementation (algorithm)
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Data Abstraction
separates the logical properties of a data type from its implementation
LOGICAL PROPERTIES IMPLEMENTATION
What are the possible values? How can this be done in C++?
What operations will be needed? How can existing data types be used?
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Data Type
set of values(domain)
allowable operationson those values
FOR EXAMPLE, data type short has
domain
-32768 . . . 32767
operations
+, -, *, /, %, >>, <<
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Abstract Data Type
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Abstract Data Type (ADT)
a data type whose properties (domain and operations) WHAT
are specified independently of any particular implementation HOW
FOR EXAMPLE . . .
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ADT Specification Example (Properties)
TYPETimeType
DOMAIN
Each TimeType value is a time in hours, minutes, and seconds.
OPERATIONSSet the time
Print the time
Increment by one second
Compare 2 times for equality
Determine if one time is “less than” another
Notice NO Implementation given!!
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Another ADT Specification
TYPEComplexNumberType
DOMAIN
Each value is an ordered pair of real numbers (a, b) representing a + bi.
OPERATIONSInitialize the complex number
Write the complex number
Add
Subtract
Multiply
Divide
Determine the absolute value of a complex number
Notice NO Implementation given!!
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ADT Implementation means
choosing a specific data representation for the abstract data using data types that already exist (built-in or programmer-defined)
writing functions for each allowable operation
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10 45 27
Several Possible Representations of TimeType
3 int variables
3 strings
3-element int array
actual choice of representation depends on time, space, and algorithms needed to implement operations
10 45 27
“10” “45” “27”
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Some Possible Representationsof ComplexNumberTypestruct with 2 float members
2-element float array
-16.2 5.8
-16.2 5.8
.real .imag
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Classes
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C++ Data TypesC++ Data Types
structured
array struct union class
address
pointer reference
simple
integral enum
char short int long bool
floating
float double long double
Class A structured type
(many components, access to each) in a programming language used to represent an ADT
Not a passive data structure (only being acted upon)
An active data structure containing data & operations in a single unit
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class TimeType Specification// SPECIFICATION FILE ( timetype.h )
class TimeType // declares a class data type{ // does not allocate memory
public : // 5 public function members
void Set ( int hours , int mins , int secs ) ;void Increment ( ) ;void Write ( ) const ;bool Equal ( TimeType otherTime ) const ; bool LessThan ( TimeType otherTime ) const ;
private : // 3 private data members
int hrs ; int mins ; int secs ;
} ;
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Use of C++ data Type class
facilitates re-use of C++ code for an ADT
software that uses the class is called a client
variables of the class type are called class objects or class instances
client code uses public member functions to handle its class objects
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Client Code Using TimeType#include “timetype.h” // includes specification of the classusing namespace std ;
int main ( ){
TimeType currentTime ; // declares 2 objects of TimeType TimeType endTime ; bool done = false ;
currentTime.Set ( 5, 30, 0 ) ; endTime.Set ( 18, 30, 0 ) ; while ( ! done )
{ . . .
currentTime.Increment ( ) ;if ( currentTime.Equal ( endTime ) )
done = true ; } ;}
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class type Definition
The class definition creates a data type and names the members of the class.
It does not allocate memory for any variables of that type!
Client code still needs to declare class variables.
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C++ Data Type class represents an ADT
2 kinds of class members: data members and function members
class members are private by default
data members are generally private
function members are generally declared public
private class members can be accessed only by the class member functions (and friend functions), not by client code.
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class TimeType Specification// SPECIFICATION FILE ( timetype.h )
class TimeType // declares a class data type{ // does not allocate memory
public : // 5 public function members
void Set ( int hours , int mins , int secs ) ;void Increment ( ) ;void Write ( ) const ;bool Equal ( TimeType otherTime ) const ; bool LessThan ( TimeType otherTime ) const ;
private : // 3 private data members
int hrs ; int mins ; int secs ;
} ;
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Aggregate class Operations
built-in operations valid on class objects are:
member selection using dot ( . ) operator ,
assignment to another class variable using ( = ),
pass to a function as argument
(by value or by reference),
return as value of a function
other operations can be defined as class member functions
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2 separate files Generally Used for class Type
// SPECIFICATION FILE ( timetype .h ) // Specifies the data and function members. class TimeType { public: . . .
private: . . . } ;
// IMPLEMENTATION FILE ( timetype.cpp ) // Implements the TimeType member functions.
. . .
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Implementation File for TimeType
// IMPLEMENTATION FILE ( timetype.cpp ) // Implements the TimeType member functions.
#include “ timetype.h” // also must appear in client code #include <iostream>
. . .
bool TimeType :: Equal ( /* in */ TimeType otherTime ) const // Postcondition: // Function value == true, if this time equals otherTime // == false , otherwise { return ( (hrs == otherTime.hrs) && (mins == otherTime.mins) && (secs ==
otherTime.secs) ) ; }
. . . // see s:\cp2\cpp\time\TestTime
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Familiar Class Instances and Function Members
the member selection operator ( . ) selects either data members or function members
header files iostream and fstream declare the istream, ostream,and ifstream, ofstream I/O classes
both cin and cout are class objects and get and ignore are function members
cin.get (someChar) ;cin.ignore (100, ‘\n’) ;
these statements declare myInfile as an instance of class ifstream and invoke function member open
ifstream myInfile ;
myInfile.open ( “A:\\mydata.dat” ) ;
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Information Hiding
Class implementation details are hidden from the client’s view. This is called information hiding.
Public functions of a class provide the interface between the client code and the class objects.
clientcode
specification implementation
abstraction barrier
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Information Hiding" "... the purpose of hiding is to make inaccessible certaindetails that should not affect other parts of a system."
-- [Ross et al, 1975]
"... [I]nformation hiding: a module is characterized by theinformation it hides from other modules, which are called itsclients. The hidden information remains a secret to the clientmodules."
-- [Ghezzi et al, 1991]
"[Information hiding is] the principle that users of a softwarecomponent (such as a class) need to know only the essentialdetails of how to initialize and access the component, and do notneed to know the details of the implementation."
-- [Budd, 1991]
"The technique of encapsulating software design decisions inmodules in such a way that the module's interfaces reveal littleas possible about the module's inner workings; thus each module isa 'black box' to the other modules in
-- [IEEE, 1983]
"The process of hiding all the details of an object that do notcontribute to its essential characteristics; typically, thestructure of an object is hidden, as well as the implementationof its methods. The terms information hiding and encapsulationare usually interchangeable."
-- [Booch, 1991]
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Scope Resolution Operator ( :: ) C++ programs typically use several class types
different classes can have member functions with the same identifier, like Write( )
member selection operator is used to determine the class whose member function Write( ) is invoked
currentTime .Write( ) ; // class TimeTypenumberZ .Write( ) ; // class ComplexNumberType
in the implementation file, the scope resolution operator is used in the heading before the function member’s name to specify its class
void TimeType :: Write ( ) const{ . . .
}
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TimeType Class Instance Diagrams
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
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2
18
30
0
currentTime endTime
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Use of const with Member Functions
when a member function does not modify private data members
use const in both function prototype (specification file) heading of function implementation (implementation file)
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class TimeType Specification// SPECIFICATION FILE ( timetype.h )
class TimeType // declares a class data type{ // does not allocate
memory
public : // 5 public function members
void Set ( int hours , int mins , int secs ) ;void Increment ( ) ;void Write ( ) const ;bool Equal ( TimeType otherTime ) const ; bool LessThan ( TimeType otherTime ) const ;
private : // 3 private data members
int hrs ; int mins ; int secs ;
} ;
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Example Using const with a Member Function
void TimeType :: Write ( ) const
// Postcondition: Time has been output in form HH:MM:SS
{ if ( hrs < 10 )
cout << ‘0’ ;
cout << hrs << ‘:’ ;
if ( mins < 10 )
cout << ‘0’ ;
cout << mins << ‘:’ ;
if ( secs < 10 )
cout << ‘0’ ;
cout << secs ;
}
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Separate Compilation and Linking of Files
timetype.h
client.cpp timetype.cpp
client.obj
client.exe
timetype.obj
Compiler Compiler
Linker
#include “timetype.h”
implementation file
specification file
main program
Projects
Many program files (nodes) compiled linked
as one executable (.exe)
Project files have .dsw extensions
The project name will be the executable name
Creating a MS VC++ Project File -> New Click on Projects Tab Select Target Type:
Win 32 Console Application Enter Project Name
(becomes name of workspace folder) Modify the workspace folder’s path to r:\.. Select empty project Click OK (new folder will be created on r:) Debug Subfolder created for .obj and .exe
Adding Source Code to a MSVC++ Project
To add new source code file to currently active project:
Select File -> New Click on Files tab Select C++ Source File as the file type Enter File name Modify, if necessary, the file’s folder path Click OK
Adding Existing Files to a MSVC++ Project
To add new source code file(s) to currently active project:
Select File View in Workspace Pane (LHS) Right Click Source Files Folder Select “Add files to Folder” Browse and select files Click OK
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#define Directive
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often several program files use the same header file containing typedef statements, constants, or class type declarations--but, it is a compile-time error to define the same identifier twice
this preprocessor directive syntax is used to avoid the compilation error that would otherwise occur from multiple uses of #include for the same header file
#ifndef Preprocessor_Identifier
#define Preprocessor_Identifier . . .
#endif
Avoiding Multiple Inclusion of Header Files
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Example Using Preprocessor Directive #ifndef
// timetype .h FOR COMPILATION THE CLASS DECLARATION IN
// SPECIFICATION FILE FILE timetype.h WILL BE INCLUDED ONLY ONCE
#ifndef TIME_H
#define TIME_H // timetype .cpp // client.cpp
// IMPLEMENTATION FILE // Appointment programclass TimeType{ #include “timetype.h” #include “timetype.h”
public: . . . . . . int main ( void )
{
private: . . .
. . . }
} ;
#endif
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Constructors
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Class Constructors
a class constructor is a member function whose purpose is to INITIALIZE the private data members of a class object
the name of a constructor is always the name of the class, and there is no return type for the constructor
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Class Constructors
a class may have several constructors with different parameter lists. A constructor with no parameters is the default constructor
a constructor is implicitly invoked when a class object is declared--if there are parameters, their values are listed in parentheses in the declaration
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Specification of TimeType Class Constructors
class TimeType // timetype.h{public : // 7 function members
TimeType ( int initHrs , int initMins , int initSecs ) ; // constructor TimeType ( ) ; // default constructor
void Set ( int hours , int minutes , int seconds ) ;void Increment ( ) ;void Write ( ) const ;bool Equal ( TimeType otherTime ) const ; bool LessThan ( TimeType otherTime ) const ;
private : // 3 data members
int hrs ; int mins ; int secs ;
} ;
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Implementation of TimeType Default Constructor
TimeType :: TimeType ( )
// Default Constructor
// Postcondition:
// hrs == 0 && mins == 0 && secs == 0
{
hrs = 0 ;
mins = 0 ;
secs = 0 ;
}
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Implementation of Another TimeType Class Constructor
TimeType :: TimeType ( /* in */ int initHrs,
/* in */ int initMins,
/* in */ int initSecs )
// Constructor
// Precondition: 0 <= initHrs <= 23 && 0 <= initMins <= 59
// 0 <= initSecs <= 59
// Postcondition:
// hrs == initHrs && mins == initMins && secs == initSecs
{
hrs = initHrs ;
mins = initMins ;
secs = initSecs ;
}
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Automatic invocation of constructors occurs
TimeType departureTime ; // default constructor invoked
TimeType movieTime (19, 30, 0 ) ; // parameterized constructor
departureTime movieTime
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
0
0
0
Private data:
hrs
mins
secs
Set
Increment
Write
LessThan
Equal
19
30
0
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Why Objects?Why Objects Anyway? Object-oriented programming doesn't fundamentally add much (it doesn't lead to much
shorter programs) But, it is a style more appropriate to human psychology. Thesis: Humans as part of their basic function are highly adept at recognizing and
interacting with everyday objects. Everyday objects: Things we encounter everyday
Properties: active: not fully controlled by us, with internal evolving state. communicative: we can "send messages". encapsulated: some of the properties are not visible (though we can learn some of it
by sending messages) nested: complex objects have many object components (which in turn have object
components etc) uniquely named (more or less) Objects in OOP (Object-Oriented Programming) also have all of these features.
Conclusion: It is thus good to have programs create entities like these objects we are familiar with.
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See TimeTestwConstructor.dsw
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Microsoft Visual C++ Project Files (Keepers)
.dsp Project file .dsw Workspace file .exe Executable program
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Microsoft Visual C++ Temporary Files
Many are large and can be removed! .ilk Incremental link file .pch Precompiled header .pdb Precompiled debugging info .idb Incremental debug info .ncb Supports viewing classes .opt Workspace configuration .plg Build log file .obj Machine code translations
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