Combining Types Of Loops; Nested Do Loops - IBM TSO/E REXX User Manual

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 a certain condition is met, at which
point it stops.
quantity = 20
DO number = 1 TO 10 WHILE quantity < 50
END
The result of this example is as follows:
You can substitute a DO UNTIL loop, change the comparison operator from < to >,
and get the same results.
quantity = 20
DO number = 1 TO 10 UNTIL quantity > 50
END

Nested DO Loops

Like nested IF/THEN/ELSE instructions, DO loops can also be within other DO
loops. A simple example follows:
DO outer = 1 TO 2
END
The output from this example is:
If you need to leave a loop when a certain condition arises, use the LEAVE
instruction followed by the control variable of the loop. If the LEAVE instruction is for
the inner loop, you leave the inner loop and go to the outer loop. If the LEAVE
instruction is for the outer loop, you leave both loops.
To leave the inner loop in the preceding example, add an IF/THEN/ELSE instruction
that includes a LEAVE instruction after the IF instruction.
DO outer = 1 TO 2
quantity = quantity + number
SAY 'Quantity = 'quantity ' (Loop 'number')'
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)
quantity = quantity + number
SAY 'Quantity = 'quantity ' (Loop 'number')'
DO inner = 1 TO 2
SAY 'HIP'
END
SAY 'HURRAH'
HIP
HIP
HURRAH
HIP
HIP
HURRAH
DO inner = 1 TO 2
IF inner > 1 THEN
LEAVE inner
Using Looping Instructions
Chapter 4. Controlling the Flow Within an Exec
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