1. CE En 270 Brigham Young University Norm Jones
Loops – Lecture #2

2. Do Loops Do loops are a simple and versatile method to do looping
Generally used when you don’t know beforehand how many times you will be going through the loop

3. Do Loop Syntax OR Do While|Until condition statement(s) Loop Do
Loop While|Until condition

4. Do Loop Examples
The following VB snippets are used to start at row 4 and loop through the cells in column A until a blank (empty) cell is found
Each of the following examples achieves the same result
Start here
Stop here

5. Method 1: Do While… Dim myrow As Integer myrow = 4
Do While Cells(myrow, 1) <> ""
myrow = myrow + 1
Loop

6. Method 2: Do Until… Dim myrow As Integer myrow = 4
Do Until Cells(myrow, 1) = ""
myrow = myrow + 1
Loop

7. Method 3: Do … Loop While Dim myrow As Integer myrow = 3 Do
myrow = myrow + 1
Loop While Cells(myrow, 1) <> ""

8. Method 4: Do … Loop Until Dim myrow As Integer myrow = 3 Do
myrow = myrow + 1
Loop Until Cells(myrow, 1) = ""

9. Differences
If you put the condition at the end (Do … Loop While|Until condition) then the loop will always be executed at least once
If you put the condition at the beginning (Do While|Until condition … Loop), then the loop may be executed zero times depending on the situation

10. Infinite Loops
When writing your loops, make sure you are doing something in the code (incrementing a counter for example) that ensures that the exit condition will eventually be met
Otherwise, you will have an “infinite loop” and it will loop forever or until you kill or interrupt Excel (use Esc key)

11. Boolean Variables
Recall that a Boolean variable is a variable that has a value of either True or False
Boolean variables can be useful when writing loops

12. Example Dim myrow As Integer Dim found As Boolean myrow = 4
found = False
Do Until found
If Cells(myrow, 4) = "" Then
found = True
Else
myrow = myrow + 1
End If
Loop

13. Exit Do Statement
You can exit any "Do" loop at any time using the Exit Do statement
This kicks you out of the loop and it moves the execution to the next statement just outside the loop

14. Example Dim myrow As Integer myrow = 4 Do Until myrow = 32768
If Cells(myrow, 1) = "" Then
Exit Do
Else
myrow = myrow + 1
End If
Loop