Halting on a COBOL line only if a condition is true

Often a particular part of your program works fine for the first few thousand times, but it fails under certain conditions. You don't want to just set a line breakpoint because you will have to keep entering GO.

Example: sample COBOL program for debugging

For example, in COBVALU you want to stop at the calculation of present value only if the discount rate is less than or equal to -1 (before the exception occurs). First run COBCALC, step into COBVALU, and stop at the statement labeled  VALU1 . To accomplish this, issue these z/OS® Debugger commands at the start of COBCALC: 
AT 67 ; GO ;
CLEAR AT 67 ; STEP 4 ;
Now set the breakpoint like this: 
AT 44 IF INTEREST > -1 THEN GO ; END-IF ;
Line 44 is the statement labeled  VALU3 . The command causes z/OS Debugger to stop at line 44. If the value of INTEREST is greater than -1, the program continues. The command causes z/OS Debugger to remain on line 44 only if the value of INTEREST is less than or equal to -1.
To force the discount rate to be negative, enter the z/OS Debugger command: 
MOVE '-2 5' TO INPUT-1 ;
Run the program by issuing the GO command. z/OS Debugger halts the program at line 44. Display the contents of INTEREST by issuing the LIST INTEREST command. To view the effect of this breakpoint when the discount rate is positive, begin a new debug session and repeat the z/OS Debugger commands shown in this section. However, do not issue the MOVE '-2 5' TO INPUT-1 command. The program execution does not stop at line 44 and the program runs to completion.