Expectations

Please test all your programs carefully and include all the test cases (i.e., check-expect expressions) with your program. You must have at least 3 check-expect tests for each function, but more are often a Very Good Thing. You don’t need to go crazy and have a bazillion of them, but you do want to be thoughtful about possible cases that should be checked.

  • If there’s a numeric argument, have you checked zero as well as both positive and negative values?
  • If there’s a string argument, did you try empty strings? Fairly long strings?
  • If there’s a boolean argument, did you try both #true and #false?
  • Etc., etc., etc.

Problem 1 (5 points)

Write a function first-letter-A-or-a? that takes a string and returns #true if the first character is either A or a (an upper or lower case ‘a’).

It should pass all these tests (which you should copy/paste into your Racket file and include in what you turn in). You can add tests to this, but definitely include at least these tests.

(check-expect (first-letter-A-or-a? "AbC") #true)
(check-expect (first-letter-A-or-a? "abC") #true)
(check-expect (first-letter-A-or-a? "bcde") #false)
(check-expect (first-letter-A-or-a? "aaAAaaaa") #true)
(check-expect (first-letter-A-or-a? "a") #true)
(check-expect (first-letter-A-or-a? "A") #true)
(check-expect (first-letter-A-or-a? "w") #false)
(check-expect (first-letter-A-or-a? "&") #false)

Some tips:

  • You’ll need an if here, and maybe nested ifs.
  • You might find or useful, but you can solve it without it (at the expense of more ifs).
  • Both string-ith and string=? are likely to be useful here.

Now extend your solution so that it returns #false if the input string is empty (""). That should pass this new test as well:

(check-expect (first-letter-A-or-a? "") #false)

Problem 2 (3 exercises – 15 points)

Read the step-by-step design process in Section 3.1. Note that we write our examples as check-expects rather than in comments. Also note that for now we will skip writing a stub for simple functions, but you would want to do it for more complex ones when you are less certain about what may go into the expression in the function.

Using this structure, develop solutions to the following three exercises:

Make sure to follow all steps of the design recipe, and phrase your “expected cases” as check-expect tests.

Don’t worry about an empty string for exercises 37 and 38, but make sure that your signature is clear about expected data.

Originally written by @elenam, with subsequent modifications by @NicMcPhee