Exercise : jGRASP Debugger

You will find it useful to be able to set a breakpoint to debug your programs. Copy and paste the following code into jGRASP:

public class Numbers {
    public static void main(String[] args) {
        int number = 42;
        for (int i = 1; i <= 1000; i++) {
            number = number * 37 % 103;
        }
        int number2 = number * number;
        System.out.println("result = " + number2);
    }
}

Set a breakpoint on the statement inside the for loop (line 5). You do this by moving your cursor to the beginning of that line until you see a stop-sign icon and then clicking.

continued on the next slide...

Exercise - jGRASP Debugger

Now you can debug the program by clicking on the debug icon instead of the run icon (it is to the right of the run icon and looks like a ladybug). It will stop every time it hits line 5. Then you can examine the values of the local variables i and number. When you want it to continue, you can hit the button that looks like the standard "play" icon of a right-pointing arrow. Using this approach, fill in the table below indicating what value number has when i has the given value. Keep in mind that you are figuring out what value number has just before it executes this line of code.

`i = 1`		42
`i = 2`		9
`i = 3`		24
`i = 4`		64

continued on the next slide...

Exercise - jGRASP Debugger

Click on the stop-sign a second time to get rid of it and then set a stop on line number 7. This will allow you to find out the value of number after the loop is done executing. Again hit the "play" button to start the programming running again. What value does number have at line 7?
69