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ANSWER
Combining Types of Loops
You can combine repetitive and conditional loops to create a compound loop. The following loop is set to
repeat 10 times while the quantity is less than 50, at which point it stops.
quantity = 20
DO number=1TO10WHILE quantity < 50
quantity = quantity + number
SAY 'Quantity = 'quantity ' (Loop 'number')'
END
The result of this example is as follows:
Quantity = 21 (Loop 1)
Quantity = 23 (Loop 2)
Quantity = 26 (Loop 3)
Quantity = 30 (Loop 4)
Quantity = 35 (Loop 5)
Quantity = 41 (Loop 6)
Quantity = 48 (Loop 7)
Quantity = 56 (Loop 8)
You can substitute a DO UNTIL loop, change the comparison operator from < to >, and get the same
results.
quantity = 20
DO number=1TO10UNTIL quantity > 50
quantity = quantity + number
SAY 'Quantity = 'quantity ' (Loop 'number')'
END
Nested DO Loops
Like nested IF...THEN...ELSE instructions, DO loops can contain other DO loops. A simple example
follows:
/******************************** REXX *******************************/
/* This program uses a DO UNTIL 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 UNTIL (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 25. Possible Solution
Control Flow within a Program
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CICS TS for VSE/ESA: REXX Guide