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Chapter 10: Controlling Program Flow and Making Decisions
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Next statement are the statements that get repeated in the loop. To see how
this works, keep reading.
A For-Next example
The following example shows a For-Next loop that doesn’t use the optional
Step value or the optional Exit For statement. This routine loops 20 times and
uses the VBA Rnd function to enter a random number into 20 cells, beginning
with the active cell:
Sub FillRange()
Dim Count As Long
For Count = 0 To 19
ActiveCell.Offset(Count, 0) = Rnd
Next Count
End Sub
In this example, Count (the loop counter variable) starts with a value of 0
and increases by 1 each time through the loop. Because I didn’t specify a
Step value, VBA uses the default value (1). The Offset method uses the value
of Count as an argument. The first time through the loop, Count is 0 and
the procedure enters a number into the active cell offset by zero rows. The
second time through (Count = 1), the procedure enters a number into the
active cell offset by one row, and so on.
Because the loop counter is a normal variable, you can write code to change
its value within the block of code between the For and the Next statements.
This, however, is a very bad practice. Changing the counter within the loop
can have unpredictable results. Take special precautions to ensure that your
code does not directly change the value of the loop counter.
A For-Next example with a Step
You can use a Step value to skip some values in a For-Next loop. Here’s the
same procedure as in the preceding section, rewritten to insert random numbers
into every other cell:
Sub FillRange2()
Dim Count As Long
For Count = 0 To 19 Step 2
ActiveCell.Offset(Count, 0) = Rnd
Next Count
End Sub
This time, Count starts out as 0 and then takes on a value of 2, 4, 6, and so
on. The final Count value is 18. The Step value determines how the counter is
incremented. Notice that the upper loop value (19) is not used because the
highest value of Count after 18 would be 20, and 20 is larger than 19.
Figure 10-2 shows the result of running FillRange2 when cell B2 is the
active cell.