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 System
Module 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 the 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.