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DO UNTIL Loops
DO UNTIL loops in a flowchart appear as follows:
False
DO UNTIL
Tr ue
instruction(s)
expression
END
As REXX instructions, the flowchart example looks like:
DO UNTIL expression /* expression must be false */
instruction(s)
END
Use DO UNTIL loops when a condition is not true and you want to execute the loop until the condition is
true. The DO UNTIL loop tests the condition at the end of the loop and repeats only when the condition is
false. Otherwise, the loop executes once and ends. For example:
/******************************** REXX *******************************/
/* This program uses a DO WHILE loop to keep track of window seats */
/* in an 8-seat commuter airline. */
/*********************************************************************/
window_seats = 0 /* Initialize window seats to 0 */
passenger = 0 /* Initialize passengers to 0 */
DO WHILE (passenger < 8) & (window_seats \= 4)
/******************************************************************/
/* Continue while the program has not yet read the responses of */
/* all 8 passengers and while all the window seats are not taken. */
/******************************************************************/
PULL window /* Gets "Y" or "N" from input stream */
passenger = passenger + 1 /* Increase number of passengers by 1 */
IF window = 'Y' THEN
window_seats = window_seats+1/*Increase window seats by 1 */
ELSE NOP
END
SAY window_seats 'window seats were assigned.'
SAY passenger 'passengers were questioned.'
Figure 23. Possible Solution
Control Flow within a Program
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CICS TS for VSE/ESA: REXX Guide