Working with Constants

WORKING WITH CONSTANTS

Data whose values do not change within a certain scope should be declared as constants by using the const modifier.

The value of a constant is specified when it is declared (this process is called initialiation). Any attempts to alter the value of a constant then results in a compilation error.

Using constants instead of hard-code literal values is an excellent programming practice. This makes your code more readable and easier to be modified later on if needed.

Examples of using constants:

Const QuarterPerDollar As Integer = 4
Public Const Pi As Single = 3.14159625      'a public constant available to all modules in a workbook
Const MyName As String = "Albert Einstein"
Const Rate = 0.0525, Duration = 12          '2 constant variants

Like variables, constants have a scope:

To make a constant available within only a single procedure, declare the constant after the procedure'Sub or Function statement.

To make a constant available to all procedures in a module, declare the coonstant in the Declarations section for the module.

To make a constant available to all modules in the workbook, use the Public keyword and declare the constant in the Declarations section of any module.

Excel and VBA contain many predefined constants, which you can use without the need to declare them yourself.

The Help System lists all the predefined constants.

The following procedure uses a predefined constant xlCalculationManual to change the Calculation property of the Application object. It changes the Excel recalculation mode to manual.
```
Sun CalcManual( )
    Application.Calculation = xlCalculationManual
End Sub
```
The actual value of the predefined constant xlCalculationManual is -4135, but you do not need to this value to use the constant.