PERFORM 'N' TIMES
PERFORM VARYING WITH 'N' UNTIL OPTION
difference between perform with test before and perform with test after.
The test condition which you are specifying in the perform is checked before if you are giving "TEST BEFORE "
likewise the condition is checked after executing the loop atlease one time in "TEST AFTER "
"TEST BEFORE" will execute only if the condition is met ...
"TEST AFTER" will execute atlease one time then the condition is checked.