REXX Programming on Mainframe

ITERATE is a REXX command that skips the remaining instructions in the current DO loop iteration and immediately proceeds to the next iteration. DO UNTIL and DO WHILE are loop control structures that determine when the loop exits, not what skips within an iteration. Option D is clearly invalid.

The DROP statement in REXX releases a variable's storage, making it uninitialized. INITIALIZE sets a value rather than unassigning, DELETE is not used for variables in REXX, and variables can indeed be unassigned.

In REXX, compound variables (stacks) use stem notation where STEM.0 automatically contains the element count. Reading and counting manually is inefficient, STACK.MAX doesn't exist, and MAX is for numeric comparisons.

TIME(E) in REXX returns elapsed time in the format sssssssss.mmmmmm (seconds.microseconds). TIME() defaults to civil time, TIME(L) gives long local time, and TIME(M) returns minutes.

COMPARE returns 0 only when strings are identical - character-by-character comparison. 'white' and 'white ' differ by trailing spaces, so they don't match. 1 means strings differ, 10 or 11 are irrelevant.

REXX is typeless and dynamically typed - variables need no declaration and automatically handle alphanumeric values. DEFINE and DECLARE aren't REXX keywords for variable declaration.

|&& is the REXX operator for Exclusive OR (XOR) - it returns 1 if exactly one operand is 1, 0 otherwise. | is OR, & is AND, and there's no Exclusive AND in REXX.

DELSTACK is the REXX command to delete/remove a stack. DROP is for variables, DELETE isn't used for stacks, and stacks can be deleted.