Learn about Do While Loop in VBA
The VBA Do While Loop is used to repeat a block of code while a specified condition is true. It’s a part of VBA’s looping constructs and is particularly useful when you don’t know beforehand how many times the loop needs to execute. The loop continues to run as long as the condition remains true, and stops as soon as the condition becomes false.
A Do…While loop is used when we want to repeat a set of statements as long as the condition is true. The condition may be checked at the beginning of the loop or at the end of the loop.
Syntax:
There are two common ways to structure a Do While loop in VBA:
- Do While at the beginning (pre-test loop):
- Do While at the end (post-test loop):
condition: This is the logical expression that determines whether the loop will continue. If the condition is True, the loop continues; if it’s False, the loop ends.
Key Features:
- Do While at the beginning: Checks the condition before executing the loop body, so if the condition is false at the start, the code inside the loop may not execute even once.
- Do While at the end: Ensures the loop runs at least once because the condition is checked after executing the loop body.
Example 1: Basic Do While Loop
This loop will continue until the variable i is greater than 10.
This loop prints numbers from 1 to 10 in the Immediate Window.
Example 2: Do While at the End
This loop guarantees that the code runs at least once, regardless of the condition.
Here, the loop will exit once i reaches 5, even though the condition allows for values up to 10.
Q & A
- What is a Do While loop in VBA and how does it work?
Answer: A Do While loop in VBA repeatedly executes a block of code as long as the specified condition evaluates to True. The loop checks the condition before each iteration. If the condition is False from the start, the loop won’t execute at all.
Example:
2. How can I prevent a Do While loop from running indefinitely in VBA?
Answer: An infinite loop occurs when the condition never becomes False. To avoid this, ensure that a variable inside the loop is updated properly, so the loop condition will eventually be False.
You can also use Exit Do to force an early exit if certain criteria are met.
3. What is the difference between Do While and Do Until loops in VBA?
Answer: The main difference lies in the condition:
- Do While: Runs as long as the condition is True.
- Do Until: Runs as long as the condition is False.
Example of Do Until:
4. Can I use multiple conditions in a VBA Do While loop?
Answer: Yes, you can use multiple conditions in a Do While loop by using logical operators like And or Or.
Example:
This loop will only run when i is less than or equal to 10 and an even number.
5. How can I loop through a range of cells in Excel using a Do While loop in VBA?
Answer: You can use a Do While loop to iterate through a range of cells until you hit a blank cell or a certain condition is met. For example:
This code loops through cells in column A, displaying the value of each cell until it encounters a blank cell.
