CSC 160 Homework 5

Assigned Oct. 8, due Oct. 24

For all the programming assignments, be sure to follow the design recipe. Write your function contract, examples, and function definition in the Definitions Window, save it to a file, and send me this file. Also test your program: since you've already included examples in the Definitions window, you should be able to hit the Execute button and see all the results (along with what you said they "should be"). Save the resulting Interactions window to a text file and send me this file too. Be sure to choose meaningful names for functions and parameters, and watch for opportunities to re-use functions you (or the textbook) have already written.

Also turn in a log of how many errors of different kinds you encountered in the assignment, with brief comments describing each one ("mismatched parentheses" is self-explanatory, but more complex errors might need more description). You may do this using the PSP forms, or simply by keeping track in a text file and turning it in.

If you think any of the assignments are ambiguous, e.g. it's not clear what value to use in a borderline case, ask me. Failing that, think about what answer makes the most sense, and then tell me your interpretation (and why you chose that way) in a comment.

This assignment is to be done in pairs, just like previous homeworks, but with a different partner.

The assignment

• Develop a function within-radius? that takes in two posns and a number, and tells whether the posns are within that distance of one another. (Note: the function does not draw any pictures on the screen. It will help to write the distance function first, taking two posns and returning the distance between them as a number.)

• Develop a function in-box? that takes in two posns and two numbers. The first posn is a location on the screen that you want to know about; the second is the top left corner of a rectangle; the first number is the width of the rectangle; and the second number is the height of the rectangle. Your function should tell whether or not the first posn is inside the rectangle specified by the other three parameters. Hint: You'll need a lot of test cases, because there are a lot of different reasons a posn might be outside the box: too far right, too far left, too far up, too far down....

• Develop a function named shift-posn that takes in a posn and two numbers x-difference and y-difference and returns another posn just like it but with the x and y coordinates increased by x-difference and y-difference respectively.

  Develop a function named draw-dot that takes in a posn and draws a small green dot centered at that position. Test it both on posns that you specify and by composing it with wait-for-mouse-click. (Since these tests are graphics-based, there's no "test run" to turn in; I'll test them myself interactively.)

  Develop a function named draw-offset-dot that takes in a posn and draws a small green dot 25 pixels to the right and 12 pixels down from it. Test it both on posns that you specify and by composing it with wait-for-mouse-click. (Since these tests are graphics-based, there's no "test run" to turn in; I'll test them myself interactively.)

• Write a function named pick-color that takes in a number (0, 1, 2, or 3) and returns one of the symbols 'red, 'green, 'blue, or 'yellow respectively.

  Write a function named random-color that takes in a symbol, ignores it, and returns one of the symbols 'red, 'green, 'blue, or 'yellow chosen at random. (Hint: you'll need to use the built-in random function. Look it up in the DrScheme Help Desk.)

  Write a function named random-posn that takes in two numbers, width and height, and returns a posn whose x coordinate is chosen randomly between 0 and width, and whose y coordinate is chosen randomly between 0 and height.

  Write a function named draw-random-ball that takes in two numbers width and height and draws a small circle of a random color in a random location. Like most of our drawing functions, this one returns true. Test your function by making a graphics window with (start 400 300), then calling (draw-random-ball 400 300) several times from the interactions window.

• Do supplementary problem 6.7. Note that the function assumes that certain variables, like WIDTH, HEIGHT, BAR-WIDTH, X1, etc. are defined; make sure you define all of these to suitable numbers in your definitions window.

  Try to write this in such a way that

  • no "magic number" appears more than once,
  • no "magic number" appears in a function definition at all, and
  • if you change the variables HEIGHT and WIDTH, but nothing else, the resulting picture will still look good: the width of the bar chart is WIDTH-20, the bars are centered in the remaining space, each bar is one quarter of the remaining space, etc.
  For hints on how to do this, look at Figure 8 of the textbook. You'll also need the hint about "Combining Effects" on p. 57 of the textbook.

Grading standards

Error log:       /30

General skills:

Total:         /450