Exercise : jGRASP Debugger

• Download the file TriangleCount.java to your machine and open it with jGrasp.
• This program explores patterns of digits for what are called the triangle numbers. The program counts how many times a triangle number ends in a particular 2-digit sequence. For example, the 15th triangle number is 120, which ends in the 2-digit sequence 20.
• Run the program and you will see a pattern: Most counts are 0 and most of the rest are exactly 200. Which 2-digit sequences have a count of 500?

  3

  28

  53

  78

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Exercise - jGRASP Debugger

• The program prints a progress dot every 200 iterations. Set a breakpoint on the System.out.print inside the if on line 23 and debug the program.
• Once the program pauses, click and drag the array at left named count, and drop it on the main code window. This will show a view of its contents.
     
• What are the first eight element values stored in the count array?

  index	0	1	2	3	4	5	6	7
  value	4	4	0	10	0	4	4	0

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Exercise - jGRASP Debugger

• Leave the array viewer open and click the Resume button . (This runs until the second time the System.out.print is about to execute, then stops.)
• What values do the first 8 array elements have now?

  index	0	1	2	3	4	5	6	7
  value	8	8	0	20	0	8	8	0

• This is a very long array with 100 total values.
  Scroll to the far right in the array viewer. What values do the last 8 elements have?

  index	92	93	94	95	96	97	98	99
  value	0	0	0	8	8	0	0	0