Declaring and Scoping of Variables

If you read the previous topics, you now know a bit about Variables and Data-types.

In this topic, you discover how to declare a variable as a certain data type.

If you don’t declare the data type for a variable you use in a VBA routine, VBA uses the default data type: Variant.

Data stored as a Variant acts like a chameleon; it changes type depending on what you do with it.

For example, if a variable is a Variant data type and contains a text string that looks like a number (such as “123”), you can use this variable for string manipulations as well as numeric calculations.

VBA automatically handles the conversion. Letting VBA handle data types may seem like an easy way out — but remember that you sacrifice speed and memory.

Before you use variables in a procedure, it’s an excellent practice to declare your variables — that is, tell VBA each variable’s data type.

Declaring your variables makes your program run faster and use memory more efficiently.

The default data type, Variant, causes VBA to repeatedly perform time consuming checks and reserve more memory than necessary.

If VBA knows a variable’s data type, it doesn’t have to investigate and can reserve just enough memory to store the data.

To force yourself to declare all the variables you use, include the following as the first statement in your VBA module:

Option Explicit

When this statement is present, you won’t be able to run your code if it contains any undeclared variables.

You need to use Option Explicit only once: at the beginning of your module, prior to the declaration of any procedures in the module.

Keep in mind that the Option Explicit statement applies only to the module in which it resides.

If you have more than one VBA module in a project, you need an Option Explicit statement for each module.

Suppose that you use an undeclared variable (that is, a Variant) named myDimension.

At some point in your routine, you insert the following statement:

myDimnsion = 11

This misspelled variable, which is difficult to spot, will probably cause your routine to give incorrect results.

If you use Option Explicit at the beginning of your module (forcing you to declare the myDimension variable), VBE generates an error if it encounters a misspelled variation of that variable.

To ensure that the Option Explicit statement is inserted automatically whenever you insert a new VBA module; turn on the Require Variable Definition option.

You find it in the Editor tab of the Options dialog box (in the VBE, choose Tools -> Options).

I highly recommend doing so.

Declaring your variables also lets you take advantage of a shortcut that can save some typing.

Just type the first two or three characters of the variable name, and then press Ctrl + Space.

The VBE will either complete the entry for you or — if the choice is ambiguous — show you a list of matching words to select from.

In fact, this slick trick works with reserved words and functions, too.

You now know the advantages of declaring variables, but how do you do this?

The most common way is to use a Dim statement.

Here are some examples of variables being declared:

Dim YourName as String
Dim PartLength as Long
Dim bRet as Boolean
Dim X

The first three variables are declared as a specific data type.

The last variable, X, is not declared as a specific data type, so it’s treated as a Variant (it can be anything).

Besides Dim, VBA has three other keywords that are used to declare variables:

  • Static
  • Public
  • Private

I explain more about the Dim, Static, Public, and Private keywords later on, but first I must cover two other topics that are relevant here: a variable’s scope and a variable’s life.

Recall that your code can have any number of VBA modules and a VBA module can have any number of Sub and Function procedures.

A variable’s scope determines which modules and procedures can use the variable.

Below Table describes the scopes:

VBA’s Variable’s Scope
Scope How the Variable is Declared
Procedure only By using a Dim or a Static statement in the procedure that uses the variable.
Module only By using a Dim or a Private statement before the first Sub or Function statement in the module.
All procedures in all modules By using a Public statement before the first Sub or Function statement in the module.

If you get confused keep reading next post on these topics.

Next post will be about Variable Scope.