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Loops are used to repeat an action. There are various variations of
the Do loops.
The formula of the Do While loop is:
Do While Condition
Statement(s)
Loop
This expression will execute the Statement or
statements AS LONG AS the Condition is true, as many times as the
Condition will be visited and found true. The program will first
test the Condition. If the Condition is true, the program will
execute the Statement or Statements and go back to the
Do While
statement and test the condition again. If the Condition is false,
the program will skip the Do While statement and not execute any.
Since the Do While statement tests the Condition first before
executing the Statement, sometimes you will want the program to
execute the Statement first, then go back and test the Condition.
VBScript offers a reverse to the formula, which is:
Do
Statement(s)
Loop While Condition
In this case, VBScript will execute the Statement or Statements first, then it will test the
Condition. If the
Condition is true, the program will execute the Statement again.
The program will continue this examination-execution as long as
the Condition is true. The big difference here is that even if the
Condition is false, the program will have executed the Condition
at least once.
An alternative to the Do While loop is the
Do
Until loop. Its formula is:
Do Until Condition
Statement(s)
Loop
This loop will first examine the Condition,
instead of examining whether the Condition is true, it will test
whether the Condition is false.
The other side of the Do Until loop will execute
the Statement first, then it would examine the Condition. The
formula is:
Do
Statement(s)
Loop Until Condition
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Decision Makers: The For...Next Statement
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If you don't know how many times a statement needs to be executed,
you can use one of the Do loops. But whenever you want to control
how many times a statement should be executed, the For...Next loop
offers a better alternative. The formula is:
For Counter
= Start
To End
Statement(s)
Next
Used for counting, the For
loop begins counting at
the Start point. Then it examines whether the current value (after
starting to count) is greater than End; if that's the case, the
program exits the loop. It then executes the Statement or Statements. Next, it increments the value of
Counter by 1 and
examines the condition again. This process goes on until Counter =
End.
The formula above will increment the counting by
1 at the end of each statement. If you want to control how the
incrementing processes, you can set your own, using the Step option.
Here is the formula:
For Counter
= Start
To End
Step Increment
Statement(s)
Next Counter
You can set the incrementing value to your
choice. If the value of Increment is positive, the Counter will be
added its value. This means you can give it a negative value, in
which case the Counter will be subtracted the set value.
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Decision Makers: The For Each...Next Statement
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Since the For Next loop is used to execute a group of statements
based on the current result of the loop counting from Start to
End,
an alternative is to state various steps in the loop and execute a
group of statements for each one of the elements in the group. This
is mostly used when dealing with a collection of items.
The formula is:
For Each Element
In Group
Statement(s)
Next Element
The loop will execute the Statement or Statement(s) for each
Element in the Group.
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