Generally, when a program runs, one instruction after another executes,
starting with the first and ending with the last. The language processor,
unless told otherwise, executes instructions sequentially.
You can change the order of execution within a program by using REXX
instructions that cause the language processor to skip some instructions,
repeat others, or transfer control to another part of the program.
These REXX instructions can be classified as follows:
- Conditional instructions set up at least one condition in the
form of an expression. If the condition is true, the language processor
selects the path following that condition. Otherwise the language
processor selects another path. The REXX conditional instructions
are:
- IF expression THEN...ELSE
- SELECT WHEN expression...OTHERWISE...END
- Looping instructions tell the language processor to repeat a set
of instructions. A loop can repeat a specified number of times or
it can use a condition to control repeating. REXX looping instructions
are:
- DO repetitor...END
- DO WHILE expression...END
- DO UNTIL expression...END
- Interrupt instructions tell the language processor to leave the program entirely
or leave one part of the program and go to another part, either permanently
or temporarily. The REXX interrupt instructions are:
- EXIT
- SIGNAL label
- CALL label...RETURN