Chapter 2Chapter 2

C# Basics

WRITING A PROGRAM• The creation of a simple console application is

given as follows.

o Step 1 Open Visual Studio and create a new console application. Write the name of the project and start the project. Figure 2.2 shows the screen that appears when you go to

o File → New → Project.o Step 2 The screen shown in Fig. 2.3 appears when you click

OK. In the Main method, write the following code.o Console.WriteLine("This moment belongs to me");

o The statement displays the text ‘This moment belongs to me’, when you run the program.

o Step 3 Run the program either by pressing F5 or by using the menu bar or toolbar.

PROGRAM STRUCTURE

• A C# program contains many sections.• Documentation

• A C# program begins with a optional documentation section.• This section may contain information about the

program, procedure used, author, date, time, and so on. It is important when you are writing a professional programs.

• The next part of a program is the using directive(s).

• The using directive qualifies the use of a namespace so that the namespace need not be written repeatedly in the program.

• The directives help us use the classes, which in turn help us connect to an access database.

• Examples : • using System;• using System.Collections.Generic;• using System.Linq;

PROGRAM STRUCTURE

ERROR

METHODS OF WRITING STATEMENTS

• Writing a statement in a single line or splitting the statement and writing it in multiple lines is the same as far as C# is concerned.

• Listing 1static void Main(string[] args){System.Console.WriteLine("Hi there");Console.ReadKey();}

• OutputHi there

INTERFACE

• An interface contains methods but not their definitions.

• An interface is a blueprint of what is to be done and does not state not how it is to be done.

• The methods declared in an interface are defined in the class that implements it.

• The syntax of an interface is as follows:interface <name of the interface>{

//Method, properties, index, or events}

• If an interface student is to have a method called getdata(), then the following code needs to be written in the editor:

interface student{void getdata(){}}

• The interface section of the program contains various interfaces that the programmer wants to use in the program.

CLASS DEFINITION• The class definition section of the program contains

the definition of a class.

• A class is a real or conceptual entity, which has importance to problem at hand.

• An instance of a class is called an object.

• Consequently, the whole concept of object-oriented programming (OOP) originates from the idea of a class.

NAMESPACES

• C# has a lot of predefined classes with functionalities; examples are input–output, data handling, and networking..

• The grouping together of classes makes organization easy.

• For example, • The evaluation of social status, impact of education,

and upliftment of a section of society may be under• Different departments, but all the departments come

under the department of social welfare

OUTPUT• The output is essential in a program as it is required

both in taking input from the user and displaying the output.

• In C#, output is displayed by using the Console.WriteLine() method.

• The WriteLine() method is in the class Console.• For example, Console.WriteLine ("Hi"); displays Hi.

Console.Write() method can be used if it is not required to display the statement in a new line. Readers

INPUT

• In C#, every input is taken as a string.• The string, in turn, is converted into the

requisite data type.• For example, if the user is asked to enter a

number, which is to be inserted into an integer variable, then the following statement performs the requisite task:

Console.WriteLine("Enter the first number\t:");

number1 = int.Parse(Console.ReadLine());

• The whole statement, however, needs to be placed in the try block, as the value entered by the user may not be an integer.

• It is enough to remember that any integer input has to be

placed in a try block and with every try block there has to be a catch block, which handles the exceptions.

int number1;try{Console.WriteLine("Enter the first number\t:");number1 = int.Parse(Console.ReadLine());Console.ReadKey();}catch(Exception e){Console.WriteLine("Error" + e.ToString());Console.ReadKey();}

MAIN METHOD• The class is contained in a namespace whose name is the

same as that of the program.• Example:

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace BasicProgram1{ class Program{static void Main(string[] args) {System.Console.WriteLine("Hi there");Console.ReadKey();} } }

CONCEPT OF Main METHOD

• When a program is executed, the first method that runs is ‘Main’.

• In order to call Main, an instance of the class in which Main is called has to be made if the method is not static.

• Static methods are those methods that have only one copy.

• They can be called by writing the name of the class followed by the name of the method, thus making things easy for the compiler.

In general, the return type of Main is void, as it does not return anything.

However, in some cases, the Main method can also return a value.

For example, assume that the requirement of the project in question is that Main should return 0 on successful completion. For this to happen, the return type of Main should be int.

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace MyConsoleApplication{class Program{static int Main(string[] args){

int number1;try{Console.WriteLine("Enter the number\t:");number1 = int.Parse(Console.ReadLine());Console.WriteLine("You have entered" + number1.ToString());Console.ReadKey();}catch(Exception e){Console.WriteLine("Error" + e.ToString());Console.ReadKey();}return 0;} }

MULTIPLE Main METHODS IN A PROGRAM

• It is possible to have a Main in each class.

• In such cases, so as to run a particular Main, one needs to make some changes in the properties of the project.

• For example, in the next program, the Main of Program class runs when the program is executed.

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace BasicProgram1{class Program{static void Main(string[] args){System.Console.WriteLine("Hi there");Console.ReadKey();}}}class ABC {static void Main(string[] args)

{System.Console.WriteLine("Hi");Console.ReadKey();}}

• It should be set equal to the name of the class whose Main is required to run.

•In order to make the Main of class ABC run when the program is executed, the name of the startup object should be changed in the properties of the program

USING SPECIFIC FUNCTIONS

• At times, it becomes essential to use mathematical functions or the functions defined in other namespaces.

• In order to do so, the using directive must be written at the beginning of the program to include the namespace whose function is to be used in the program or the method should be called by qualifying the name of the namespace as well.

• Program:using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace MyConsoleApplication{class Program{static void Main(string[] args){int number1, number2;double result;

try{Console.WriteLine("Enter the first number\t:");number1 = int.Parse(Console.ReadLine());Console.WriteLine("Enter the second number\t:");number2 = int.Parse(Console.ReadLine());result = Math.Sqrt((−1.0 * number2) / number1);Console.WriteLine("The result is" + result.ToString());Console.ReadKey(); }catch(Exception e) {Console.WriteLine("Error" + e.ToString());Console.ReadKey(); }}}}

COMMENTS

• Comments are the statements that are not executed when the program runs.

• They are important as far as documentation is concerned and are essential to understand the program.

• It may be noted that a project is handled not by a single person but by a team.

• Comments are written in two ways:1. Single-line comments2. Multiple-line comments

• It may be stated that comments are not considered in software metrics such as lines of code (LOC). However, this does not diminish their importance.

SINGLE-LINE COMMENTS• Single-line comments are generally preceded by ‘//’,

as shown in the following listing.

• Example//Using directives [ Single-line comment]using System;using System.Collections.Generic;using System.Linq;using System.Text;//namespace [->Single-line comment]namespace MyConsoleApplication{…..

MULTIPLE-LINE COMMENTS

• At times, the explanation of some of the methods might take more than one line.

• The comment is preceded by a ‘/*’ and ends with a ‘*/’.

using System;using System.Collections.Generic;using System.Linq;using System.Text;/*namespaceThe name is same as that of the program*/

COMMAND LINE ARGUMENTS

• The arguments given in Main are stored in the array args.

• When command line arguments are given, these arguments can be handled as normal array elements.

• However, it may be stated that a simple for loop is capable of traversing through the array

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace MyConsoleApplication{class Program{static int Main(string[] args){for(int i=0;i<args.Length;i++){Console.WriteLine("Argument" + args[i]);}Console.ReadKey();return 0; } }}

• The command line arguments can be given in the Debug tab of the properties of the project. In

• Order to do so, right click on the name of the namespace in Solution Explorer and enter the command line arguments in ‘Start Options’.

• The output of the program will be as follows:

COMPILATION PROCESS

• The process of compilation has five main steps, namely lexical analysis, syntactic analysis, semantic analysis, intermediate code generation, and code generation.

• The semantic analysis segregates the program into tokens. These tokens are identified by the reduced deterministic finite acceptor.

• Lets take an example of an identifier which starts with a letter and is followed by any number of letters or digits:

• The regular expression of an identifier will be l(l + d)*, where l is a letter and d is a digit.

• This regular expression is converted• into a non-deterministic finite acceptor.

COMPILATION PROCESS

• The steps to convert the regular expression into a deterministic finite acceptor are as follows:

• In the first step, the non-deterministic finite acceptor for (l + d) is made. Here, l and d can be accepted by the automata by two parallel paths.

• This is followed by the formation of the non-deterministic finite acceptor for (l + d)*. Here, * denotes repetition.

• From the second symbol onwards, an identifier may have any number of letters or digits; therefore, the initial and the final states of the automata are connected via a null move. That is, one can go from the initial to the final state without giving any input.

• This step is followed by the formation of automata l(l + d)*.

• In the next step, this automata is converted into a deterministic finite acceptor.

• It is an acceptor as it accepts or rejects. It tells us whether the input string is an identifier or not.

• This process is called lexical analysis. It may be noted that most of the common errors are reported by this phase of the compiler.

• This step is followed by the syntactic and semantic analyses. The syntactic analysis checks the syntax, whereas the semantic analysis checks the semantics and interprets the meaning of the construct.

• The intermediate code generation generates the intermediate code, which is a step towards the final machine level code generation..

• The error handling mechanism is necessary at every phase of the compilation process.

• The following are some instances that result in an error:

1. Misspelt Keyword•It is the job of a lexical analyser to check whether a keyword has been spelt correctly. It is done•with the help of a deterministic finite acceptor as explained earlier.2. Syntactic Error•An example of syntactic error is the absence of closing parenthesis in an ‘if condition’. The•lexical analyser identifies such errors with the help of parse trees.3. Incompatible Operands to an Operator•The intermediate code generator identifies this type of errors. Such errors become all the more•important in C# as it intends to overcome such shortcomings in C and C++.

4. Multiple Declarations of an Identifier• The bookkeeping routine helps identifying such errors.• There can be many more sources of errors. When a program is

compiled, the errors will be shown in the error list. This displays the line number, a brief description of the error, and the error code. The screenshot given in the following figure depicts the error in an error pane.

POINTS TO REMEMBER

• Main method section is the most important and mandatory component of a C# program.

• Main method in C# is public, is static, and has return type ‘void’.

• There can be more than one Main method in C# program.

• In order to carry out specialized mathematical tasks, the program should have System.Math namespace.

• Comments are not executed when program runs.

• The command line arguments can be given in the Debug tab of the properties of the project.

• The process of compilation has five main steps, namely lexical analysis, syntactic analysis, semantic analysis, intermediate code generation, and code generation.

POINTS TO REMEMBER