In VBA, a constant is a value that cannot be changed during the execution of a program. Unlike variables, constants are assigned a value once, and that value remains fixed throughout the code. Using constants is useful when you need to use specific, unchanging values repeatedly.
Constant is a named memory location used to hold a value that CANNOT be changed during the script execution. If a user tries to change a Constant value, the script execution ends up with an error.
How to Declare a Constant in VBA
You declare a constant in VBA using the Const keyword, followed by the name of the constant and its value.
Example:
Syntax:
Example:
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Explanation:
- TAX_RATE is a constant of type Double, representing a fixed tax rate.
- MAX_AGE is an integer constant used for comparing an age limit.
- COMPANY_NAME is a string constant that stores the name of the company.
Example Code Using Constants:
In this example, the constant TAX_RATE is used to calculate the net salary after tax. Since the tax rate doesn’t change, it’s defined as a constant for clarity and efficiency.
Example of Using Constants in a Program:
In this example, the constant Pi is used to calculate the circumference of a circle. Since the value of Pi never changes, it’s more efficient to use a constant than a variable.
Key Points about Constants:
- Fixed Value: Once assigned, the value of a constant cannot be changed during program execution.
- Data Types: Like variables, constants can have data types such as Integer, String, Double, etc.
- Naming: By convention, constant names are often written in all uppercase letters to distinguish them from variables (e.g., PI, DAYS_IN_WEEK).
Benefits of Using Constants:
- Readability: Improves the readability of your code by giving meaningful names to fixed values.
- Maintenance: Easier to maintain since you only need to update the value in one place if it ever changes.
- Code Clarity: Descriptive constant names make the code easier to understand (e.g., using PI instead of 3.14159 everywhere).
- Prevents Accidental Changes: Since constants can’t be modified during program execution, it reduces the risk of accidental changes to values that should remain fixed.
- Efficiency: Constants can improve performance slightly, as VBA knows their value won’t change.
Constants vs. Variables:
- Constants: Values do not change during program execution. Ideal for fixed values like tax rates, pi, or company information.
- Variables: Can change as your program runs, useful for data that varies, like user inputs or calculations.
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