ITEC 380 2016fall ibarland

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hw02
defining functions
hw02

Due: Sep.12 (Mon) 14:00, on D2L and hardcopy.
Your submitted file should be named “hw02.rkt” as plain-text (which is what DrRacket saves as).

Standard instructions for all homeworks:

• Your name, the assignment-number, and the URL of this assignment-page must be in a comment at the start of the file.
• Any code which results in syntax errors will generally not earn more than 50% of the points-possible. For grading, I will ignore any commented-out code (including commented-out tests).
• If your hardcopy is more than 1page, it must be stapled.
• Format well. (In particular, each open-paren should be preceded by a space or start-of-line, for now. E.g. (+ 2 (* 3 4 5)), not ( + 2(* 3 4
  5)
  ).)

1. (10pts) Recall from lecture, we demo'd the steps of writing a simple function, pizza-area, which computed the area of a pizza given diameter. We will write a couple of similar functions.

   Of course, Pizzas have topping in the middle, and crust around the edge. (You can think of the full pizza being a disc, with a smaller pure-topping-covered disc inside of it.)

   1. Define a named-constant CRUST-WIDTH, which should be 2 inches.
   2. Some people ignore the crust of a pizza, and just want to know how much topping-covered area they'll be getting when they order a pizza. Write topping-area, which returns the amount of pizza covered in topping (in square-inches), for a given diameter (in inches).
   3. Other people love the crust, and only care about how much crust is on their pizza! Write crust-area, which returns the amount of crust (in square-inches) for a pizza of a given diameter (in inches).

   For now, your code does not need to give a correct answer for pizzas whose diameter is less than twice the CRUST-WIDTH. However, you should still have tests for that situation, which contain the true, expected answer in the check-expect.

   (So, it's fine if those tests don't pass. If you really want to get your code working for that case -- again, NOT required -- you can either read about cond, or be clever in using the functions max or min.)

2. (10pts) Write the function has-suffix?, which takes in two strings and returns whether or not the first string ends with (the letters of) the second.

   Note that this is a computer-sciency definition of “suffix”. It has nothing to do with syllables or English. More precisely: we say that string a has b as a suffix, iff: there exists a string x such that (string=? a (string-append x b)).

   hint:You can certainly use cond (or if) if you like, but they're not actually needed; you can instead use a min or max in a clever (but standard) way.

   Friday: We will mention if in class on Friday.

conditions/requirements

In addition to the standard instructions for all hws above, here are some requirements for our homeworks:

• For every functions you write, follow the design recipe, steps 4,5,7,8. (You don't need to label each step; just turn in the final result.) When grading, there are points for having a good purpose-statement, good tests, etc. In general, test cases alone can be worth nearly half the points.

• Your programs should be racket's beginning-student language (for now).
• Don't repeat code!
  For example: If you find yourself repeating similar calculations to what's already in pizza-area, see if you can avoid the repeated calculations by calling pizza-area as a helper-function (perhaps a couple of times).

home—lectures—recipe—exams—hws—D2L—breeze (snow day; distance)

©2016, Ian Barland, Radford University Last modified 2016.Sep.16 (Fri)

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