Constants

Often, you'll find that your macro contains constant values that reappear again and again. Or you may find that the macro depends on certain numbers that are difficult to remember — numbers that, in and of themselves, have no obvious meaning.

In these cases, you can greatly improve the readability of your macro — and make it easier to maintain — by using constants. A constant is a meaningful name that takes the place of a number or string that doesn't change. Although a constant somewhat resembles a variable, you cannot modify a constant or assign a new value to it as you can do with a variable. There are two sources for constants:

• Built-in constants — also called intrinsic or system-defined constants — are provided by applications. Microsoft Excel constants are listed in the Microsoft Excel object library in the Object Browser. Other applications that provide object libraries, such as Microsoft Access and Microsoft Project, also provide a list of constants you can use with their objects, methods, and properties. For information about using the Object Browser, see Chapter 4, "Objects and Collections."

  Intrinsic constant names have a mixed-case format, with a two-character prefix indicating the object library that defines the constant. Constants from the Microsoft Excel object library are prefaced with "xl" — for instance, xlAbsolute. Constants from the data access object library are prefaced with "db" — for instance, dbRelationUnique.

• Symbolic constants, or user-defined constants, are declared with the Const statement. User-defined constants are described in the next section, "Declaring User-Defined Constants."

Tip

Use constants when you need to use the same value several times in your macro, or when you want to make your macro more readable by assigning a meaningful name to a value that doesn't change.