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Homework 2

Assigned Feb 4, due Feb 18

Pair Programming

You are encouraged to do this assignment in a two-student team, following the principles of Pair Programming. This does not mean "you do these problems and I'll do those"; it means both students work together, looking over one another's shoulders, to complete all the problems. Turn in one copy with both names on it. I recommend that you choose a different partner for the next homework assignment, so if you don't get along with this partner, remember it's only for a week :-)

Meeting

Again, please make an appointment for a meeting in my office. This time the purpose of the meeting isn't “get to know you” but rather “demonstrate that you can define a function”. It will be a simple example, but I want to see, with my own eyes, that every student in the class has had the experience of defining a working function, following the design recipe, before we go on to chapter 6.

Problems

You are to write six complete function definitions, and parts of two others. (That's one every two days. The first few you do will probably take a while, but once you get used to defining functions, they should take only a few minutes each.) Follow the design recipe!

• Warm-up (not graded): Try all of the "Worked Exercises" and "Practice Exercises" as you get to them: either type them in from the book, or download them from here, then run them and make sure they do what you expect.
• Warm-up (not graded):Exercises 1.5.2 through 1.5.5
• Warm-up (not graded):Exercises 3.5.2 through 3.5.11
• Exercise 4.2.2, the four-square function.
Note: This exercise is in chapter 4, before the Design Recipe had been introduced, so you're not strictly required to use the recipe. But it's still a good idea!
• Exercises 4.3.1 and 4.3.2: identify parameters and arguments in function definitions (print out the definitions on paper, then draw circles or boxes on the paper).
• Develop the checkerboard2 function: the contract is provided in worked exercise 5.3.4, so you should do examples (5.4.3), skeleton (5.8.3), inventory (5.9.4), body (5.11.3), and testing (5.12.1).
• Write a contract, examples, skeleton, and inventory for the copies-beside function (exercises 5.3.2, 5.4.2, 5.8.1, 5.9.2). Writing the body requires techniques you don't know yet.
• Develop the bullseye function: contract (exercise 5.3.5), examples (5.4.5), skeleton (5.8.4), inventory (5.9.5), body (5.11.4), and testing (5.12.1).
• Write a contract, examples, skeleton, and inventory for the dot-grid function (exercises 5.3.6, 5.4.6, 5.8.5, 5.9.6). Again, writing the body requires techniques you don't know yet.
• Develop the lollipop function: contract (5.3.7), examples (5.4.7), skeleton (5.8.6), inventory (5.9.7), body (5.11.5), and testing (5.12.1).
• Develop a checkerboard4 function that takes in two color names (like checkerboard2) and produces a 4x4 checkerboard in those colors. Follow all the steps of the design recipe, in order. Hint: if your definition is more than three lines long, you're doing it the hard way. Re-use previously-defined functions!
• Do one of the exercises 5.14.1 through 5.14.5 (your choice; in any case, do all the steps of the design recipe)

What to turn in and how

For exercises 4.3.whatever, I suggest printing out the definitions on paper, then circling and labeling parts of them with pencil or pen. You can also do it on the computer if you prefer.

For the programming problems, I want to see all the steps of the recipe. I recommend putting all of the programming problems in one big Definitions pane; by the time you're done, the contract, definition (including skeleton, inventory, and body), and examples of each function should be together, looking like Figure 5.2 of the textbook.

It's difficult for me to grade your testing of these functions, but be assured that I will test them, and if they don't work, it'll hurt your grade, so it's to your advantage to test them before turning them in.

Send me an e-mail, attaching the file containing your saved Definitions pane. (Make sure to save it, then test it, then e-mail it to me, or I may end up grading an out-of-date version.) Make sure to put your name in the Subject line!

If there's a particular function that you can't get working, turn in as many steps of the recipe as you've managed to do, commented out (so they don't mess up the other functions).

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). Note that "errors" means not only error messages from DrScheme, but also wrong answers. You may do this using the PSP forms, or simply by keeping track in a text file or on paper and turning it in.

General advice

For all assignments in chapters 5 and later, be sure to follow the design recipe. (It couldn't hurt for the problems in chapter 4 either, but it's not required.)

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.

Grading standards

In order to get you feedback quickly, I won't actually grade all of these problems; the rest should be considered practice.

Error log:       25 points
(I'm not grading on how many or how few errors you encountered, only on whether you recorded them correctly.)

Box-diagram exercises:     10 points each
Argument/parameter exercises:     10 points each

The table below has columns for each step in the design recipe, and a row for each function that I decide to grade. You won't turn in a separate skeleton, inventory, and body, but rather write a skeleton and then add inventory and body to turn it into a complete definition. However, if you don't get the definition working, you'll still get partial credit for a correct contract, skeleton, and/or inventory.

General skills:

Total:         /???