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Part III: Programming Concepts
Sub DoUntilDemo()
Do Until IsEmpty(ActiveCell.Value)
ActiveCell.Value = ActiveCell.Value * 2
ActiveCell.Offset(1, 0).Select
Loop
End Sub
Just like with the Do-While loop, you may encounter a different form of the
Do-Until loop — a Do-Loop Until loop. The following example, which has the
same effect as the preceding procedure, demonstrates an alternate syntax for
this type of loop:
Sub DoLoopUntilDemo()
Do
ActiveCell.Value = ActiveCell.Value * 2
ActiveCell.Offset(1, 0).Select
Loop Until IsEmpty(ActiveCell.Value)
End Sub
There is a subtle difference in how the Do-Until loop and the Do-Loop Until
loop operate. In the former, the test is performed at the beginning of the loop,
before anything in the body of the loop is executed. This means that it is possible
that the code in the loop body will not be executed if the test condition
is met. In the latter version, the condition is tested at the end of the loop.
Therefore, at a minimum, the Do-Loop Until loop always results in the body of
the loop being executed once.
Another way to think about it is like this: The Do-While loop keeps looping as
long as the condition is True. The Do-Until loop keeps looping as long as the
condition is False.
Looping through a Collection
VBA supports yet another type of looping — looping through each object in a
collection of objects. Recall that a collection consists of a number of objects
of the same type. For example, Excel has a collection of all open workbooks
(the Workbooks collection), and each workbook has a collection of worksheets
(the Worksheets collection).
When you need to loop through each object in a collection, use the For Each-
Next structure. The syntax is
For Each element In collection
[statements]
[Exit For]
[statements]
Next [element]