Access Database Design and Programming, Second Edition

Chapter 11. Functions and Subroutines

VBA allows two kinds of procedures: functions and subroutines. The only difference between a function and a subroutine is that a function returns a value, whereas a subroutine does not.

Calling Functions

A function declaration has the form:

[Public or Private] Function FunctionName(Param1 As DataType1, _
         Param2 As DataType2,...) As ReturnType

Note that we must declare the data types not only of each parameter to the function, but also of the return type. Otherwise, VBA declares these items as variants.

We will discuss the optional keywords Public and Private later in this chapter, but you can probably guess that they are used here to indicate the scope of the function, just as they are used in variable declarations.

For example, the AddOne function in Example 11.1 adds 1 to the original value.

Example 11-1. The AddOne Function

Public Function AddOne(Value As Integer) As Integer
   AddOne = Value + 1
End Function

To use the return value of a function, we just place the call to the function within the expression, in the location where we want the value. For instance, the code:

MsgBox "Adding 1 to 5 gives: " & AddOne(5)

produces the message box in Figure 11.1, where the expression AddOne(5) is replaced by the return value of AddOne, which in this case is 6.

Figure 11-1. The message dialog displayed by Example 11-1

Note that, in general, any parameters to a function ...