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How to: Declare A Constant (Visual Basic)

  • Άρθρο

You use the Const statement to declare a constant and set its value. By declaring a constant, you assign a meaningful name to a value. Once a constant is declared, it cannot be modified or assigned a new value.

You declare a constant within a procedure or in the declarations section of a module, class, or structure. Class or structure-level constants are Private by default, but may also be declared as Public, Friend, Protected, or Protected Friend for the appropriate level of code access.

The constant must have a valid symbolic name (the rules are the same as those for creating variable names) and an expression composed of numeric or string constants and operators (but no function calls).

Note

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To declare a constant

  • Write a declaration that includes an access specifier, the Const keyword, and an expression, as in the following examples:

    Public Const DaysInYear = 365
Private Const WorkDays = 250

    When Option Infer is Off and Option Strict is On, you must declare a constant explicitly by specifying a data type (Boolean, Byte, Char, DateTime, Decimal, Double, Integer, Long, Short, Single, or String).

    When Option Infer is On or Option Strict is Off, you can declare a constant without specifying a data type with an As clause. The compiler determines the type of the constant from the type of the expression. For more information, see Constant and Literal Data Types.

To declare a constant that has an explicitly stated data type

  • Write a declaration that includes the As keyword and an explicit data type, as in the following examples:

    Public Const MyInteger As Integer = 42
Private Const DaysInWeek As Short = 7
Protected Friend Const Funday As String = "Sunday"

    You can declare multiple constants on a single line, although your code is more readable if you declare only a single constant per line. If you declare multiple constants on a single line, they must all have the same access level (Public, Private, Friend, Protected, or Protected Friend).

To declare multiple constants on a single line

  • Separate the declarations with a comma and a space, as in the following example:

    Public Const Four As Integer = 4, Five As Integer = 5, Six As Integer = 44

See also