Until

See Also: Boolean Expressions, Execution Control Commands, For, Loop, Repeat, While, Break, Boolean

Purpose

Establishes a conditional terminator for repeating blocks of code initiated with Repeat or While.

Syntax

repeat
    ... commands ...
until {expression}

What It Does

The until command sends execution back to the last previous repeat command until the test expression becomes true. When the test becomes true, execution proceeds to the command following the until command.

Procedure AddRecs
    String sName sAddress sPhone
    repeat
        readln sName sAddress sPhone // will set SeqEof if end of file
        If not (SeqEOF) ;
            Send SaveNewRecord sName sAddress sPhone
    until (SeqEOF)
End_Procedure

In this example, the loop keeps executing until the end of the sequential file is encountered. This represents normal usage of this command. SeqEOF is the sequential end of file indicator.

Procedure AddRecs
    Integer iCount
    String sName sAddress sPhone
    move 0 to iCount
    repeat
        readln sName sAddress sPhone
        Send SaveNewRecord sName sAddress sPhone
        increment iCount
    until (iCount > 100)
End_Procedure

In this example, the loop keeps executing until the variable iCount becomes greater than or equal to 100, at which point execution moves to the next statement (end_procedure).

A repeat ... until block will always execute at least once.

You may make until subject to "compound" conditionals.

Procedure AddRecs
    Integer iCount
    String sName sAddress sPhone
    move 0 to iCount
    repeat
        readln sName sAddress sPhone
        If not (SeqEOF) begin
            Send SaveNewRecord sName sAddress sPhone
            increment iCount
        end
    until (SeqEOF or (iCount > 100))
End_Procedure

SeqEOF is the sequential end of file indicator.

Notes

• The statements inside blocks are usually indented to make the blocks more readable.
• A variable or expression with a value of zero (0) is the test equivalent of false. A variable with a value other than zero is the test equivalent of true.
• Until can also be used with statement blocks that were started with for or while, although such usage is considered to be unusual.