.net programming

List of Available Modifiers in VB.Net

Declaring Constants

[ < attributelist> ] [ accessmodifier ] [ Shadows ] 
Const constantlist

• attributelist: specifies the list of attributes applied to the constants; you can provide multiple attributes separated by commas. Optional.
• accessmodifier: specifies which code can access these constants. Optional. Values can be either of the: Public, Protected, Friend, Protected Friend, or Private.
• Shadows: this makes the constant hide a programming element of identical name in a base class. Optional.
• Constantlist: gives the list of names of constants declared. Required.

constantname [ As datatype ] = initializer

• constantname: specifies the name of the constant
• datatype: specifies the data type of the constant
• initializer: specifies the value assigned to the constant

'The following statements declare constants.'
Const maxval As Long = 4999
Public Const message As String = "HELLO" 
Private Const piValue As Double = 3.1415

Example

Module constantsNenum
   Sub Main()
      Const PI = 3.14149
      Dim radius, area As Single
      radius = 7
      area = PI * radius * radius
      Console.WriteLine("Area = " & Str(area))
      Console.ReadKey()
   End Sub
End Module

Area = 153.933

Print and Display Constants in VB.Net

Declaring Enumerations

[ < attributelist > ] [ accessmodifier ]  [ Shadows ] 
Enum enumerationname [ As datatype ] 
   memberlist
End Enum

• attributelist: refers to the list of attributes applied to the variable. Optional.
• asscessmodifier: specifies which code can access these enumerations. Optional. Values can be either of the: Public, Protected, Friend or Private.
• Shadows: this makes the enumeration hide a programming element of identical name in a base class. Optional.
• enumerationname: name of the enumeration. Required
• datatype: specifies the data type of the enumeration and all its members.
• memberlist: specifies the list of member constants being declared in this statement. Required.

[< attribute list>] member name [ = initializer ]

• name: specifies the name of the member. Required.
• initializer: value assigned to the enumeration member. Optional.

Enum Colors
   red = 1
   orange = 2
   yellow = 3
   green = 4
   azure = 5
   blue = 6
   violet = 7
End Enum

Example

Module constantsNenum
   Enum Colors
      red = 1
      orange = 2
      yellow = 3
      green = 4
      azure = 5
      blue = 6
      violet = 7
   End Enum
   Sub Main()
      Console.WriteLine("The Color Red is : " & Colors.red)
      Console.WriteLine("The Color Yellow is : " & Colors.yellow)
      Console.WriteLine("The Color Blue is : " & Colors.blue)
      Console.WriteLine("The Color Green is : " & Colors.green)
      Console.ReadKey()
   End Sub
End Module

The Color Red is: 1
The Color Yellow is: 3
The Color Blue is: 6
The Color Green is: 4

Variable Declaration in VB.Net

[ < attributelist> ] [ accessmodifier ] [[ Shared ] [ Shadows ] | [ Static ]]
[ ReadOnly ] Dim [ WithEvents ] variablelist

• attributelist is a list of attributes that apply to the variable. Optional.
• accessmodifier defines the access levels of the variables, it has values as - Public, Protected, Friend, Protected Friend and Private. Optional.
• Shared declares a shared variable, which is not associated with any specific instance of a class or structure, rather available to all the instances of the class or structure. Optional.
• Shadows indicate that the variable re-declares and hides an identically named element, or set of overloaded elements, in a base class. Optional.
• Static indicates that the variable will retain its value, even when the after termination of the procedure in which it is declared. Optional.
• ReadOnly means the variable can be read, but not written. Optional.
• WithEvents specifies that the variable is used to respond to events raised by the instance assigned to the variable. Optional.
• Variablelist provides the list of variables declared.

variablename[ ( [ boundslist ] ) ] [ As [ New ] datatype ] [ = initializer ]

• variablename: is the name of the variable
• boundslist: optional. It provides list of bounds of each dimension of an array variable.
• New: optional. It creates a new instance of the class when the Dim statement runs.
• datatype: Required if Option Strict is On. It specifies the data type of the variable.
• initializer: Optional if New is not specified. Expression that is evaluated and assigned to the variable when it is created.

Dim StudentID As Integer
Dim StudentName As String
Dim Salary As Double
Dim count1, count2 As Integer
Dim status As Boolean
Dim exitButton As New System.Windows.Forms.Button
Dim lastTime, nextTime As Date

Variable Initialization in VB.Net

variable_name = value;

Dim pi As Double
pi = 3.14159

Dim StudentID As Integer = 100
Dim StudentName As String = "Bill Smith"

Example

Module variablesNdataypes
   Sub Main()
      Dim a As Short
      Dim b As Integer
      Dim c As Double
      a = 10
      b = 20
      c = a + b
      Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c)
      Console.ReadLine()
   End Sub
End Module

a = 10, b = 20, c = 30

Accepting Values from User

Dim message As String
message = Console.ReadLine

Module variablesNdataypes
   Sub Main()
      Dim message As String
      Console.Write("Enter message: ")
      message = Console.ReadLine
      Console.WriteLine()
      Console.WriteLine("Your Message: {0}", message)
      Console.ReadLine()
   End Sub
End Module

Enter message: Hello World   
Your Message: Hello World

Lvalues and Rvalues

• lvalue : An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.
• rvalue : An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

Dim g As Integer = 20

20 = g