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Chapter: C# and .NET Framework

Program Structure and Simple Input and Output Operations

Let us look at a simple code that prints the words "Hello World": using System;


A C# program consists of the following parts:


·        Namespace declaration

·        A class

·        Class methods

·        Class attributes

·        A Main method

·        Statements and Expressions

·        Comments


Let us look at a simple code that prints the words "Hello World": using System;


namespace HelloWorldApplication



class HelloWorld


static void Main(string[] args)



/* my first program in C# */ Console.WriteLine("Hello World"); Console.ReadKey();






When this code is compiled and executed, it produces the following result: Hello World


Let us look at the various parts of the given program:


Ø    The first line of the program using System; - the using keyword is used to include the System namespace in the program. A program generally has multiple using statements.


Ø    The next line has the namespace declaration. A namespace is a collection of classes. The HelloWorldApplication namespace contains the class HelloWorld.


Ø    The next line has a class declaration, the class HelloWorld contains the data and method definitions that your program uses. Classes generally contain multiple methods. Methods define the behavior of the class. However, the HelloWorld class has only one method Main.


Ø    The next line defines the Main method, which is the entry point for all C# programs. The Main method states what the class does when executed.

Ø    The next line /*...*/ is ignored by the compiler and it is put to add comments in the program.


Ø    The Main method specifies its behavior with the statement Console.WriteLine("Hello World");


Ø    WriteLine is a method of the Console class defined in the System namespace. This statement causes the message "Hello, World!" to be displayed on the screen.

Ø    The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is


launched from Visual Studio .NET.

You can compile a C# program by using the command-line instead of the Visual Studio IDE:

·        Open a text editor and add the above-mentioned code.

·        Save the file as helloworld.cs

·        Open the command prompt tool and go to the directory where you saved the file.

·        Type csc helloworld.cs and press enter to compile your code.


·        If there are no errors in your code, the command prompt takes you to the next line and generates helloworld.exe executable file.


·        Type helloworld to execute your program.

·        You can see the output Hello World printed on the screen.


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