Microsoft Office

VBA Examples 44
If you don’t declare a variable, Excel uses the Variant data type. In general, the best technique is to use
the data type that uses the smallest number of bytes yet can still handle all the data assigned to it. An exception
is when you’re performing floating-point calculations. In such a case, it is always best to use the
Double data type (rather than the Single data type) to maintain maximum precision.
When VBA works with data, execution speed is a function of the number of bytes that VBA has at its disposal.
In other words, the fewer bytes that are used by data, the faster VBA can access and manipulate the
data.
To declare a variable, use the Dim statement before you use the variable for the first time. For example, to
declare the variable Units as an integer, use the following statement:
Dim Units as Integer
To declare the variable UserName as a string, use the following statement:
Dim UserName as String
If you declare a variable within a procedure, the declaration is valid only within that procedure. If you
declare a variable outside of any procedures (but before the first procedure), the variable is valid in all procedures
in the module.
If you use an object variable (as described in “Simplifying object references,” earlier in this chapter), you can
declare the variable as the appropriate object data type. The following is an example:
Dim Rate as Range
Set Rate = Workbooks(“MyBook.xlsx”).Worksheets(“Sheet1”).Range(“IntRate”)
To force yourself to declare all the variables that you use, insert the following statement at the top of your
module:
Option Explicit
If you use this statement, Excel displays an error message if it encounters a variable that hasn’t been
declared. After you get into the habit of correctly declaring all your variables, you will find that it helps
eliminate errors and makes spotting errors easier.
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