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In the previous lessons, we explored variables and how to declare them in VBA. In this section, we’ll discuss the concept of a Constant and see why and how you should use constants in your VBA code.

What Is a Constant in VBA?

Sometimes, we use values in VBA that remain the same throughout the program and appear repeatedly — for example, a tax rate, a profit percentage, or a specific file path. In such cases, it’s better to use constants instead of writing numbers or text directly into the code.

Using constants makes your code easier to read, more maintainable, and less error-prone. Essentially, a constant provides a meaningful name for a value that does not change while the program is running.

For example, if you write the tax rate directly in several places in your code and later the rate changes, you would need to review and update the entire project. However, if you use a constant, you only need to update its value in one place.

Unlike variables, the value of a constant cannot be changed while the program is running.

According to the VBA Glossary, a constant in VBA is a named element whose value does not change during program execution.

Types of Constants in VBA

• Intrinsic Constants: These are built-in constants provided by VBA or its libraries (such as Excel, Access, or Word). You can view them using the Object Browser.
• Symbolic Constants: These are constants you define yourself using the Const statement. This is the main focus of this tutorial.
• Conditional Compiler Constants: These are defined using the #Const directive and are used to control parts of the code at compile time.

💡 Tip: Visual Basic continues to support constants from earlier versions, so you don’t need to redeclare them.

How to Declare a Constant in VBA

To define a constant, use the Const keyword. The general syntax is as follows:

Const ConstantName As DataType = Value

For example, suppose you want to specify a tax rate as a constant in your program:

Public Const VAT_RATE As Double = 0.09

In this example, the public constant VAT_RATE represents a 9% tax rate, and it can be used anywhere in your VBA project.

Constant Scope in VBA

You can declare constants either at the procedure level or at the top of a module. If you declare a constant at the top of a module, it is Private by default.

Difference Between a Constant and a Variable

• The value of a constant is assigned once when declared and cannot be changed later.
• A variable is declared using Dim and its value can change during program execution.
• Using constants helps reduce errors and improves code readability.

Declaring Multiple Constants in One Line

You can declare several constants in one Const statement, but the data type of each constant must be specified separately:

Const conAge As Integer = 34, conWage As Currency = 35000

If a constant’s value is a string, it must be enclosed in quotation marks (" "). For example:

Const COMPANY_NAME As String = "IranVBA Academy"

⚠️ Common Errors:
• You cannot assign a variable’s value to a constant.
• A constant’s value cannot be modified at runtime.

References (Microsoft Docs):

Declaring Constants
Using Constants in VBA