常数（Const）

如果你的应用程序中的值永远不会更改，则可以定义命名常量并使用它来代替文字值。

你只能在模块或过程级别使用 Const。这意味着变量的声明上下文必须是类，结构，模块，过程或块，并且不能是源文件，命名空间或接口。

Public Const GLOBAL_CONSTANT As String = "Project Version #1.000.000.001"
Private Const MODULE_CONSTANT As String = "Something relevant to this Module"

Public Sub ExampleDeclaration()    

    Const SOME_CONSTANT As String = "Hello World"
    
    Const PI As Double = 3.141592653

End Sub

虽然指定常量类型可以被认为是一种好的做法，但并不是严格要求的。不指定类型仍将导致正确的类型：

Public Const GLOBAL_CONSTANT = "Project Version #1.000.000.001" 'Still a string
Public Sub ExampleDeclaration()

    Const SOME_CONSTANT = "Hello World"           'Still a string
    Const DERIVED_CONSTANT = SOME_CONSTANT        'DERIVED_CONSTANT is also a string
    Const VAR_CONSTANT As Variant = SOME_CONSTANT 'VAR_CONSTANT is Variant/String
    
    Const PI = 3.141592653        'Still a double
    Const DERIVED_PI = PI         'DERIVED_PI is also a double
    Const VAR_PI As Variant = PI  'VAR_PI is Variant/Double
    
End Sub

请注意，这是特定于常量，而不是指定类型的变量导致 Variant 类型的变量。

虽然可以将常量显式声明为 String，但不可能使用固定宽度字符串语法将常量声明为字符串

'This is a valid 5 character string constant
Const FOO As String = "ABCDE"

'This is not valid syntax for a 5 character string constant
Const FOO As String * 5 = "ABCDE"