Sub and Function Procedures

The VBA code that you write in the Visual Basic Editor is known as a procedure.

The two most common types of procedures are Sub and Function.

  • A Sub procedure is a group of VBA statements that performs an action (or actions).
  • A Function procedure is a group of VBA statements that performs a calculation and returns a single value.

Most of the macros you write in VBA are Sub procedures.

You can think of a Sub procedure as being like a command: “Execute the Sub procedure and something happens”.

Exactly what happens depends on the Sub procedure’s VBA code.

A Function is also a procedure, but it’s quite different from a Sub.

For understanding a Function let’s take an example from MS Excel.

Excel includes many worksheet functions that you use every day. Examples include SUM. This SUM function takes input in form of values and then it does calculation behind the scene, and then returns a single value.

The same goes for Function procedure that you develop with VBA.

Sub procedures

Every Sub procedure starts with the keyword Sub and ends with an End Sub statement. Here’s an example:

Sub Message()
   MsgBox "That’s all folks!"
End Sub

This example shows a procedure named Message. A set of parentheses follows the procedure’s name.

In most cases, these parentheses are empty. However, you may pass arguments to Sub procedures from other procedures.

If your Sub uses arguments, list them between the parentheses.

Please remember when you record a macro with the macro recorder; the result is always a Sub procedure.

Function procedures

Every Function procedure starts with the keyword Function and ends with an End Function statement.

Here’s an example:

Function CubeRoot(number)
   CubeRoot = number ^ (1/3)
End Function

This function, named CubeRoot, takes one argument (named number), which is enclosed in parentheses.

Functions can have any number of arguments or none at all.

When you execute the function, it returns a single value — the cube root of the argument passed to the function.

VBA allows you to specify what type of information (also known as data type) is returned by a Function procedure.

You can execute a Function procedure from another procedure (a Sub or another Function procedure).

Please note that no matter how hard you try, you can’t use the macro recorder to record a Function procedure. You must manually enter every Function procedure that you create.

Naming Subs and Functions

Like humans & pets, every Sub and Function procedure must have a name.

Although it is perfectly acceptable to name anything what you want, it’s usually not a good idea to use such a freewheeling attitude when naming procedures.

When naming procedures, you must follow a few rules:

  • You can use letters, numbers, and some punctuation characters, but the first character must be a letter.

  • You can’t use any spaces or periods in the name.

  • VBA does not distinguish between uppercase and lowercase letters.

  • You can’t embed any of the following characters in a procedure name: #, $, %, &, @, ^, *, or !

  • Procedure names can be no longer than 255 characters. (Of course, you would never make a procedure name this long.)

Ideally, a procedure’s name describes the routine’s purpose.

Some programmers prefer using sentence-like names that provide a complete description of the procedure.

Some examples include WriteReportToTextFile and Get_Print_Options_and_Print_Report.

The use of such lengthy names has pros and cons.

On the one hand, such names are descriptive and usually unambiguous. On the other hand, they take longer to type.

Everyone develops a naming style, but the main objectives are to make the names descriptive and to avoid meaningless names such as Update, Fix, and Macro1.

Next post will be about Executing Sub & Function procedures.