Mini-project – “Stopwatch: The Game”


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Our mini-project for this week will focus on combining text drawing in the canvas with timers to build a simple digital stopwatch that keeps track of the time in tenths of a second. The stopwatch should contain “Start”, “Stop” and “Reset” buttons. To help guide you through this project, we suggest that you download the provided program template for this mini-project and build your stopwatch program as follows:

Mini-project development process

  1. Construct a timer with an associated interval of 0.1 seconds whose event handler increments a global integer. (Remember that create_timertakes the interval specified in milliseconds.) This integer will keep track of the time in tenths of seconds. Test your timer by printing this global integer to the console. Use the CodeSkulptor reset button in the blue menu bar to terminate your program and stop the timer and its print statements. Important:Do not use floating point numbers to keep track of tenths of a second! While it’s certainly possible to get it working, the imprecision of floating point can make your life miserable. Use an integer instead, i.e., 12 represents 1.2 seconds.
  2. Write the event handler function for the canvas that draws the current time (simply as an integer, you should not worry about formatting it yet) in the middle of the canvas. Remember that you will need to convert the current time into a string using strbefore drawing it.
  3. Add “Start” and “Stop” buttons whose event handlers start and stop the timer. Next, add a “Reset” button that stops the timer and reset the current time to zero. The stopwatch should be stopped when the frame opens.
  4. Next, write a helper function format(t)that returns a string of the form A:BC.D where A, C and D are digits in the range 0-9 and B is in the range 0-5. Test this function independent of your project using this testing template (Just cut and paste your definition of  format into the template.) Note that the string returned by your helper functionformat should always correctly include leading zeros. For example
    • format(0) = 0:00.0
    • format(11) = 0:01.1
    • format(321) = 0:32.1
    • format(613) = 1:01.3

Hint: Use integer division and remainder (modular arithmetic) to extract various digits for the formatted time from the global integer timer.

  1. Insert a call to the formatfunction into your draw handler to complete the stopwatch. (Note that the stopwatch need only work correctly up to 10 minutes, beyond that its behavior is your choice.)
  2. Finally, to turn your stopwatch into a test of reflexes, add to two numerical counters that keep track of the number of times that you have stopped the watch and how many times you manage to stop the watch on a whole second (1.0, 2.0, 3.0, etc.). These counters should be drawn in the upper right-hand part of the stopwatch canvas in the form “x/y”where x is the number of successful stops and y is number of total stops. My best effort at this simple game is around a 25% success rate.
  3. Add code to ensure that hitting the “Stop” button when the timer is already stopped does not change your score. We suggest that you add a global Boolean variable that is Truewhen the stopwatch is running and False when the stopwatch is stopped. You can then use this value to determine whether to update the score when the “Stop” button is pressed.
  4. Modify “Reset” so as to set these counters back to zero when clicked.

Steps 1-3 and 5-7 above are relatively straightforward. However, step 4 requires some adept use of integer division and modular arithmetic. So, we again emphasize that you build and debug the helper function format(t) separately following the tips in the Code Clinic page linked below. Following this process will save you time. For an example of a full implementation, we suggest that you watch the video lecture on this mini-project.

For more helpful tips on implementing this mini-project, please visit the Code Clinic tips page for this mini-project.

Grading Rubric – 13 pts total (scaled to 100 pts)

  • 1 pt – The program successfully opens a frame with the stopwatch stopped.
  • 1 pt – The program has a working “Start” button that starts the timer.
  • 1 pt – The program has a working “Stop” button that stops the timer.
  • 1 pt – The program has a working “Reset” button that stops the timer (if running) and resets the timer to 0.
  • 4 pts – The time is formatted according to the description in step 4 above. Award partial credit corresponding to 1 pt per correct digit. For example, a version that just draw tenths of seconds as a whole number should receive 1 pt. A version that draws the time with a correctly placed decimal point (but no leading zeros) only should receive 2 pts. A version that draws minutes, seconds and tenths of seconds but fails to always allocate two digits to seconds should receive 3 pts.
  • 2 pts – The program correctly draws the number of successful stops at a whole second versus the total number of stops. Give one point for each number displayed. If the score is correctly reported as a percentage instead, give only one point.
  • 2 pts – The “Stop” button correctly updates these success/attempts numbers. Give only one point if hitting the “Stop” button changes these numbers when the timer is already stopped.
  • 1 pt – The “Reset” button clears the success/attempts numbers.

In the submission phase, cut and paste the URL for your cloud-saved mini-project into the box below. Click the Honor Code box and hit the “Submit for grading” button when you are ready to submit your mini-project.  (You may submit as many times as you like before the deadline so we suggest that you use “Submit” instead of “Save”.)  IMPORTANT: Please use the “Review your work” link that appears at the top of the subsequent submission page to verify that you submitted a working link for the final version of your mini-project.