VBScript in a Nutshell, 2nd Edition

Name

Do . . . Loop Statement

Syntax

Do [{While | Until} condition]
   [statements]
[Exit Do]
   [statements]
Loop

or:

Do
   [statements]
[Exit Do]
   [statements]
Loop [{While | Until} condition]

condition

Use: Optional

Data Type: Boolean expression

An expression that evaluates to True or False.

statements

Use: Optional

Program statements that are repeatedly executed while, or until, condition is True.

Description

Repeatedly executes a block of code while or until a condition becomes True.

Rules at a Glance

• On its own, Do...Loop repeatedly executes the code that is contained within its boundaries indefinitely. You therefore need to specify under what conditions the loop is to stop repeating. Sometimes, this requires modifying the variable that controls loop execution within the loop. For example:

  Do
     intCtr = intCtr + 1   ' Modify loop control variable
     Response.Write "Iteration " & intCtr & _
            " of the Do loop..." & "<BR>"
     ' Compare to upper limit
     If intCtr = 10  Then Exit Do   
  Loop

  Failure to do this results in the creation of an endless loop.

• Adding the Until keyword after Do instructs your program to Do something Until the condition is True. Its syntax is:

  Do Until condition
                             code to execute
  Loop

  If condition is True before your code gets to the Do statement, the code within the Do...Loop is ignored.

• Adding the While keyword after Do repeats the code while a particular condition is True. When the condition becomes False, the loop is automatically exited. The syntax of the Do While statement is:

  Do While condition