CSC 160 HW4

Assigned 27 Feb, due 13 March

Note: For the functions "check-guess", "check-color", etc. you are expected to test the functions directly as usual, and turn in the resulting test run, as well as testing them with the teachpack (for which there's really nothing to turn in). For the graphics problems in section 6.2, you'll need to test these yourself, one at a time, using the Interactions window; there is nothing to turn in for test runs.

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).

This assignment is to be done in pairs, just like homework 3 (but with a different partner).

This is a long assignment. I'm giving you two weeks to do it, and you'll need two weeks; start immediately!

• Do (but don't turn in) as many of the exercises in section 4.1, section 4.2, and section 4.3 as you think you need.
• Do exercise 4.4.2 in How to Design Programs.
• Do exercise 4.4.3 in How to Design Programs.
• Develop a function ebay-commission to compute the commission E-Bay charges on an auction. Here are the rules:

  The commission is the sum of an "insertion fee" and a "final value fee". The insertion fee, which depends on the asking price, is computed as follows:

  • If the asking price is $0.01-$9.99, the fee is $.30.
  • If the asking price is $10.00-$24.99, the fee is $.55.
  • If the asking price is $25.00-$49.99, the fee is $1.10.
  • If the asking price is $50.00-$199.99, the fee is $2.20.
  • If the asking price is $200.00 or more, the fee is $3.30.

  The final value fee, which depends on the selling price, is computed as follows:

  • Compute 5% of the amount up to $25.00.
  • If the selling price is over $25.00, add 2.5% of the amount over $25.00 up to $1000.00.
  • If the selling price is over $1000.00, add 1.25% of the amount over $1000.00.
  For example, if the selling price were $20.00, the final value fee would be $1.00.
  If the selling price were $40.00, the final value fee would be $1.625: 5% of the first $25 makes $1.25, and 2.5% of the next $15 makes $.375.
  If the selling price were $2000.00, the final value fee would be 5% of the first $25, or $1.25, plus 2.5% of the next $975, or $24.375, plus 1.25% of the remaining $1000, or $12.50, for a total of $38.125.

  Hint: You'll almost certainly need to write more than one function. Each of your functions must have a contract, examples, etc. In the past, when I've assigned similar problems, many students (especially the more experienced ones) skipped through the "contract" part, got it wrong, and everything after that was hopeless. The moral is follow the design recipe!

  Note: I don't think E-Bay actually charges fractional cents; they round the commission to the nearest cent. You're not required to do that for this assignment.

• Do exercise 5.1.2 in How to Design Programs. Test it by playing the game as described in the textbook.
• Do exercise 5.1.3 in How to Design Programs. Test it by playing the game as described in the textbook.
• Do exercise 5.1.5 in How to Design Programs. Test it by playing the game as described in the textbook.
• Do all the problems in section 6.2.