Language Support

The exercises and code samples in this tutorial demonstrate how to use C#, Visual Basic, and JScript to build .NET applications. For information regarding the syntax of the other languages, refer to the complete documentation for the .NET Framework SDK.

The following table is provided to help you understand the code samples in this tutorial as well as the differences between the three languages:

Variable Declarations

Dim x As Integer
Dim s As String
Dim s1, s2 As String
Dim o 'Implicitly Object
Dim obj As New Object()
Public name As String

Statements

Response.Write("foo")

Comments

' This is a comment

' This
' is
' a
' multiline
' comment

Accessing Indexed Properties

Dim s, value As String
s = Request.QueryString("Name")
value = Request.Cookies("Key").Value

'Note that default non-indexed properties
'must be explicitly named in VB

Declaring Indexed Properties

' Default Indexed Property
Public Default ReadOnly Property DefaultProperty(Name As String) As String
    Get
        Return CStr(lookuptable(Name))
    End Get
End Property

Declaring Simple Properties

Public Property Name As String

  Get
    ...
    Return ...
  End Get

  Set
    ... = Value
  End Set

End Property

Declare and Use an Enumeration

' Declare the Enumeration
Public Enum MessageSize

    Small = 0
    Medium = 1
    Large = 2
End Enum

' Create a Field or Property
Public MsgSize As MessageSize

' Assign to the property using the Enumeration values
MsgSize = small

Enumerating a Collection

Dim S As String
For Each S In Coll
 ...
Next

Declare and Use Methods

' Declare a void return function
Sub VoidFunction()
 ...
End Sub

' Declare a function that returns a value
Function StringFunction() As String
 ...
    Return CStr(val)
End Function

' Declare a function that takes and returns values
Function ParmFunction(a As String, b As String) As String
 ...
    Return CStr(A & B)
End Function

' Use the Functions
VoidFunction()
Dim s1 As String = StringFunction()
Dim s2 As String = ParmFunction("Hello", "World!")

Custom Attributes

' Stand-alone attribute
<STAThread>

' Attribute with parameters
<Obsolete("Obsolete message here")>

' Attribute with named parameters
<Obsolete("Obsolete message here", true)>

Arrays

    Dim a(2) As String
    a(0) = "1"
    a(1) = "2"
    a(2) = "3"

    Dim a2(2,2) As String
    a(0,0) = "1"
    a(1,0) = "2"
    a(2,0) = "3"

Initialization

Dim s As String = "Hello World"
Dim i As Integer = 1
Dim a() As Double = { 3.00, 4.00, 5.00 }

If Statements

If Not (Request.QueryString = Nothing)
  ...
End If

Case Statements

Select Case FirstName
  Case "John"
    ...
  Case "Paul"
    ...
  Case "Ringo"
    ...
  Case Else
    ...
End Select

For Loops

  Dim I As Integer
  For I = 0 To 2
    a(I) = "test"
  Next

While Loops

Dim I As Integer
I = 0
Do While I < 3
  Console.WriteLine(I.ToString())
  I += 1
Loop

Exception Handling

Try
    ' Code that throws exceptions
Catch E As OverflowException
    ' Catch a specific exception
Catch E As Exception
    ' Catch the generic exceptions
Finally
    ' Execute some cleanup code
End Try

String Concatenation

' Using Strings
Dim s1, s2 As String
s2 = "hello"
s2 &= " world"
s1 = s2 & " !!!"

' Using StringBuilder class for performance
Dim s3 As New StringBuilder()
s3.Append("hello")
s3.Append(" world")
s3.Append(" !!!")

Event Handler Delegates

Sub MyButton_Click(Sender As Object,
                   E As EventArgs)
...
End Sub

Declare Events

' Create a public event
Public Event MyEvent(Sender as Object, E as EventArgs)

' Create a method for firing the event
Protected Sub OnMyEvent(E As EventArgs)
    RaiseEvent MyEvent(Me, E)
End Sub

Add or Remove Event Handlers to Events

AddHandler Control.Change, AddressOf Me.ChangeEventHandler
RemoveHandler Control.Change, AddressOf Me.ChangeEventHandler

Casting

Dim obj As MyObject
Dim iObj As IMyObject
obj = Session("Some Value")
iObj = CType(obj, IMyObject)

Conversion

Dim i As Integer
Dim s As String
Dim d As Double

i = 3
s = i.ToString()
d = CDbl(s)

' See also CDbl(...), CStr(...), ...

Class Definition with Inheritance

Imports System

Namespace MySpace

  Public Class Foo : Inherits Bar

    Dim x As Integer

    Public Sub New()
      MyBase.New()
      x = 4
    End Sub

    Public Sub Add(x As Integer)
      Me.x = Me.x + x
    End Sub

    Overrides Public Function GetNum() As Integer
       Return x
    End Function

  End Class

End Namespace

' vbc /out:libraryvb.dll /t:library
' library.vb

Implementing an Interface

Public Class MyClass : Implements IEnumerable
 ...

    Function IEnumerable_GetEnumerator() As IEnumerator _
        Implements IEnumerable.GetEnumerator
         ...
    End Function
End Class

Class Definition with a Main Method

Imports System

Public Class ConsoleVB

  Public Sub New()
    MyBase.New()
    Console.WriteLine("Object Created")
  End Sub

  Public Shared Sub Main()
    Console.WriteLine("Hello World")
    Dim cvb As New ConsoleVB
  End Sub

End Class

' vbc /out:consolevb.exe /t:exe console.vb

Standard Module

Imports System

Public Module ConsoleVB

  Public Sub Main()
    Console.WriteLine("Hello World")
  End Sub

End Module

' vbc /out:consolevb.exe /t:exe console.vb