Ia loop unconditionally and continues with the next clause after the loop

IF var_1 = var_2 THEN var_1 = var_1 + a loop and EXEC unconditionally, but doesn't return to the caller of the EXEC.

a loop and EXEC unconditionally, returns to the caller of the EXEC and provides a return code.

a loop and EXEC unconditionally, returns to the caller of the EXEC, but doesn't provide a return code.