VB.Net - Constants and Enumerations

• facebook

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well. The constants are treated just like regular variables except that their values cannot be modified after their definition. An enumeration is a set of named integer constants. Declaring Constants In VB.Net, constants are declared using the Const statement. The Const statement is used at module, class, structure, procedure, or block level for use in place of literal values. The syntax for the Const statement is: [ < attributelist > ] [ accessmodifier ] [ Shadows ] Const constantlist Where, 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. Where, each constant name has the following syntax and parts: 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 For example, ' The following statements declare constants. Const maxval As Long = 4999 Public Const message As String = "HELLO" Private Const piValue As Double = 3.1415 Example The following example demonstrates declaration and use of a constant value: 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 When the above code is compiled and executed, it produces the following result: Area = 153.933 Print and Display Constants in VB.Net VB.Net provides the following print and display constants: Constant Description vbCrLf Carriage return/linefeed character combination. vbCr Carriage return character. vbLf Linefeed character. vbNewLine Newline character. vbNullChar Null character. vbNullString Not the same as a zero-length string (""); used for calling external procedures. vbObjectError Error number. User-defined error numbers should be greater than this value. For example: Err.Raise(Number) = vbObjectError + 1000 vbTab Tab character. vbBack Backspace character. Declaring Enumerations An enumerated type is declared using the Enum statement. The Enum statement declares an enumeration and defines the values of its members. The Enum statement can be used at the module, class, structure, procedure, or block level. The syntax for the Enum statement is as follows: [ < attributelist> ] [ accessmodifier ] [ Shadows ] Enum enumerationname [ As datatype ] memberlist End Enum Where, 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. Each member in the memberlist has the following syntax and parts: [< attribute list>] member name [ = initializer ] Where, name: specifies the name of the member. Required. initializer: value assigned to the enumeration member. Optional. For example, Enum Colors red = 1 orange = 2 yellow = 3 green = 4 azure = 5 blue = 6 violet = 7 End Enum Example The following example demonstrates declaration and use of the Enum variable Colors: 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 When the above code is compiled and executed, it produces the following result: The Color Red is: 1 The Color Yellow is: 3 The Color Blue is: 6 The Color Green is: 4 vb.net programming