VB.Net Program Structure

Before we study basic building blocks of the VB.Net programming language, let us look a bare minimum VB.Net program structure so that we can take it as a reference in upcoming chapters.

VB.Net Hello World Example

A VB.Net program basically consists of the following parts:

• Namespace declaration
• A class or module
• One or more procedures
• Variables
• The Main procedure
• Statements & Expressions
• Comments

Let us look at a simple code that would print the words "Hello World":

Imports SystemModule Module1
   'This program will display Hello World 
   Sub Main()
      Console.WriteLine("Hello World")
      Console.ReadKey()
   End Sub
End Module

When the above code is compiled and executed, it produces following result:

Hello, World!

Let us look various parts of the above program:

• The first line of the program Imports System is used to include the System namespace in the program.
• The next line has a Module declaration, the module Module1. VB.Net is completely object oriented, so every program must contain a module of a class that contains the data and procedures that your program uses.
• Classes or Modules generally would contain more than one procedure. Procedures contain the executable code, or in other words, they define the behavior of the class. A procedure could be any of the following:
  • Function
  • Sub
  • Operator
  • Get
  • Set
  • AddHandler
  • RemoveHandler
  • RaiseEvent
• The next line( 'This program) will be ignored by the compiler and it has been put to add additional comments in the program.
• The next line defines the Main procedure, which is the entry point for all VB.Net programs. The Main procedure states what the module or class will do when executed.
• The Main procedure specifies its behavior with the statement
  Console.WriteLine("Hello World")
  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.
• The last line Console.ReadKey() is for the VS.NET Users. This will prevent the screen from running and closing quickly when the program is launched from Visual Studio .NET.

Compile & Execute VB.Net Program:

If you are using Visual Studio.Net IDE, take the following steps:

• Start Visual Studio.
• On the menu bar, choose File, New, Project.
• Choose Visual Basic from templates
• Choose Console Application.
• Specify a name and location for your project using the Browse button, and then choose the OK button.
• The new project appears in Solution Explorer.
• Write code in the Code Editor.
• Click the Run button or the F5 key to run the project. A Command Prompt window appears that contains the line Hello World.

You can compile a VB.Net 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.vb
• Open the command prompt tool and go to the directory where you saved the file.
• Type vbc helloworld.vb and press enter to compile your code.
• If there are no errors in your code the command prompt will take you to the next line and would generate helloworld.exe executable file.
• Next, type helloworld to execute your program.
• You will be able to see "Hello World" printed on the screen.