CSci 1301: Problem Set 2

Due: Wednesday, September 17 at 11:59pm by e-mail

Please test all your programs carefully and include all the test cases with your program. You should have at least 3 tests for each function, except the ones that produce an image or a scene.

Problem 1 (6 points)

Recall the function first-letter-A? that we wrote in class. Here is our code:

;; (first-letter-A? str) -> boolean
;; str: string
;; consumes a string, returns  true 
;; if this string starts with a capital A, otherwise returns false
(define (first-letter-A? str)
  (string=? (substring str 0 1) "A"))

(check-expect (first-letter-A? "AbC") true)
(check-expect (first-letter-A? "abC") false)
(check-expect (first-letter-A? "bcde") false)
;(check-expect (first-letter-A? "") false)
(check-expect (first-letter-A? "aaAAaaaa") false)

1. Add the case to handle the empty string in the function (it must return false for it, as the commented out test case indicates). You can use cond or if or (better!) combine your conditions using boolean operations, such as and, or, not (either approach will get full credit if works correctly).
   
2. Write a function first-letter-a-or-A? that returns true if this string starts with "A" or "a" and false otherwise. It must return false for an empty string. Make sure to write test cases and the description (contract) for your function.

Problem 2 (2 points)

Modify the version 5 of the landing rocket example (figure 4 in Prologue) so that when the width of the scene is changed, the rocket is placed in the middle of the new scene.

Problem 3

Exercises 24 (5 points) and 25 (5 points) in Section 2.2.

CSci 1301 course web site.