Debugging exercise

The Debugger

We will be using lab1c.cob to learn how to run the debugger.

First, check the program code and ensure that the PIC clause for the yearly interest rate is 999 and not 9V99. One edition of the book had it wrong and the sample version of the code we made available for copying also had it wrong. It needs to be 999.

In the terminal window click the top right corner button, the one that looks like a box (not the dot) to maximize your terminal window. You can toggle this button to enlarge and reduce your terminal window. You MUST maximize your terminal window to run the debugger effectively (actually, you only need to maximize the terminal window before the runcbl command). Once you have maximized your terminal window, type the following commands to first compile the program with debugging information and then to run the lab in the debugger:

ccbl -Zd lab1c.cob
runcbl -d lab1c

You will see a menu at the top of the window (press F10 to activate the menu at the top of the screen, if necessary), a source code area and a command area at the bottom. A list of debugger commands can be accessed by typing help in the command area (use the up and down arrow keys to scroll and press enter to exit the help screen). Typing q! on the command line will exit the debugger at any time. Notice that a black box exists to the left of the PERFORM statement in paragraph 000-CALCULATE-FUTURE-VALUES. This is the cursor for the debugger.

A few commands that you will use frequently are given below (do not try them yet!)

• s – single step; when you press s followed by enter the current statement will execute and the cursor in the source code area will move to the next executable statement in your program.
• d – will display the memory contents of a specified field; when you type d field-name followed by enter the value contained in that field will be shown in the command area.
• b – sets a break point so that execution will pause at a specified point in the program. However, a break point can only be set at the paragraph level (not the statement level). To use this command, you can type b parapgraph-name followed by enter.
• gp – program executes to the end of the current paragraph.
• s – program executes until you reach a break point or a STOP RUN.

Follow the next set of instructions and answer the questions:

Create a file called lab3ques.txt to hold the answers to the questions given below.

Compile the program appropriately and start the debugger

Answers to these questions are here (Word doc)

1. What is the current value of NUMBER-ENTERED?
2. Is the debugger case-sensitive?

Single step 4 times.

3. What will be the next statement (in what paragraph) to be executed?

Single step 1 more time.

4. What happened?

Single step 3 more times.

5. What will be the next statement (in what paragraph) to be executed?

You will need to single step twice to enter each set of input data. When asked, enter 10000 for the investment amount, 10 for the number of years and 100 for the yearly interest rate (remember, the program does not accept editted input. These inputs represent the values 100.00, 10 and 10.0). Once you have entered the data the debugger cursor should be to the left of the statement MOVE INVESTMENT-AMOUNT TO FUTURE-VALUE.

Single step two more times.

6. What is the current value of YEAR-COUNTER?

Set a breakpoint at paragraph 120-CALCULATE-NEXT-FV (A B should appear to the left of this paragraph name). Enter g twice.

7. What is the current value of FUTURE-VALUE?

Enter g twice more.

8. What is the current value of FUTURE-VALUE?
9. How many more times do you have to enter g before something different happens?
10. Why did you get there?

Enter 1 to perform another calculation and enter the same input information.

11. What debugger command will clear all breakpoints? Use help.

Clear all breakpoints. Type g. When asked to end the program or perform another calculation, end the program.