VBA Function vs VBA Sub

Excel VBA Function vs VBA Sub – Excel Functions and Procedures

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A VBA Function can accept parameters and return results. Functions, however, can’t be executed directly. On the other hand a VBA Sub procedure can be executed directly and can also accept parameters. Procedures, however, do not return values.

We often use Subs and Functions often not thinking about their true potential and how much we can squeeze out of a regular VBA Function. Let’s start with a reminder how both differ from each other and then dive into the details.

VBA Sub, VBA Function Syntax

Below structure resembles a VBA Sub and VBA Function:

Below are simple examples of Subs and Functions:

VBA Sub procedure syntax

The code block of a VBA Sub procedure is marked by the Sub and End Sub statements.
VBA Sub procedure

VBA Function procedure syntax

The code block of a VBA Function is marked by the Function and End Function statements.
VBA Function

VBA Function vs VBA Sub

We often tend to mix up procedures, Subs and Functions in VBA. So let’s get it right this time. There are 2 main differences between VBA Procedures (Subs) and VBA Functions:

  • VBA Functions return values, VBA Subs don’t
  • You can execute a VBA Sub, you can’t execute VBA Functions – they can only be executed by VBA Subs

Executing Functions and Subs

Although I provided examples above there are multiple ways to execute a VBA Function and a VBA Sub:

Passing arguments ByVal and ByRef

The common knowledge is that only VBA Functions can return values. That indeed is mostly true. However, instead of a value (the result of the Function), we can assign values to variables that can be passed to the procedure by reference. What does that mean?

Variables can either by passed to a procedure (Function, Sub etc.) by their value or their reference.
Passing by value translates to making a copy of the variable. Thus any changes to the copy will not be reflected in the original variable.
Passing by reference is passing the address of the variable to the procedure. This means that any changes to a argument will be reflected in the original variable.

ByVal vs ByRef
Passing a variable by its Value or its Reference

By default all arguments are passed to procedures ByVal, so that no changes can be made to the original variables

ByVal and ByRef examples

Let’s look at some examples now:

When passing by value the variable someLong is not modified. However, when we pass it by reference its value is changed within the Sub procedure.

Objects and arrays are always passed by reference, because objects are in fact references (e.g. a Collection). Beware in such cases not to modify referenced objects by mistake!

Passing arrays to Subs and Functions

You can also easily pass arrays to Subs or Functions, even redefining their length. See example below:

Optional parameters

VBA Functions and Subs permit optional parameters, ones that need not be provided when executing the Function or Sub. It is a good practice to specify the default value for such parameters. See example below:

You can verify if a parameter has not been passed to an Sub or Function by using the IsMissing function. The IsMissing function works however only for Variant type parameters. See the same SayHi procedure as above, this time with the IsMissing function.

Dynamic parameter list

Say you want to create a VBA function like the Excel SUM or AVERAGE formulas – that can be provided with a dynamic list of parameters. VBA extends a neat solution for such a scenario called the ParamArray.

The ParamArray transforms a list of Variant variables passed as parameters into a neat Variant array.