Enables repeated execution of a block of command.

Syntax

WHILE [expression]

commands

ENDWHILE

Parameters

Comments

The WHILE … ENDWHILE structure enables a block of commands to be repeatedly executed, as long as expression is logically true.

As soon as the software detects that expression is logically false, execution resumes at the first command following the ENDWHILE. To exit a loop before expression evaluates to false, use a BREAK command.

An open WHILE loop is automatically closed if

• you exit a procedure in the middle of a WHILE structure (using a BYE, RETURN, STOP, or TRANSFORM command), or
• a procedure ends before the ENDWHILE is encountered.

Example

% Commands to select and display form fDispEmp

%

——————————————————————-

find all Employees       % Create set of all Employees

while $setcount > 0      % Loop until end of set

  change fDispEmp from current  % Fill form with emp. data

  form display nolabel input    % Display form and start input

  if Event.EventName = “Escape”  % Check for Escape key

  return           % If so, finish

  endif

  if ThisForm.FormChanged = $true % Check if data modified

  change current from fDispEmp % Update current member

  endif

  next            % Go to next record

  let $setcount = $setcount – 1   % Decrement $setcount

endwhile

while Age > 20

 … other commands …

% Missing endwhile statement

… more commands …

last command in procedure

In the preceding example, the commands subsequent to the missing ENDWHILE command are executed as if they were a part of the WHILE structure. When the end of the procedure is reached without encountering the necessary ENDWHILE, it generates an error message.

form open fCustomers

while

 form display input

 … more commands …

 if Event.EventName = “Escape”

  break

 endif

…more commands …

endwhile

Notice in the preceding command that a BREAK (or BYE, RETURN, STOP, or TRANSFORM) command is required to exit a WHILE loop that contains no logic expression.

See Also

Boolean Expressions

Conditional Expressions

CONTINUE