Bubble Review

There will be some program tracing and some problem solving.

Program 1

Trace the following program to figure out what it does.

(define (prog1 n)
  (cond [(< n 5) 10]
        [(= 1 (remainder n 2)) (+ 1 (prog1 (- n 1)))]
        [(not (= 1 (remainder n 2))) (+ 3 (prog1 (- n 2)))]
        [else (+ 5 (prog1 (- n 3)))]))

1. (prog1 2)
2. (prog1 5)
3. (prog1 6)
4. (prog1 8)

Program 2

Trace the following program to figure out what it does.

(define (prog2 s)
  (cond [(< (string-length s) 2) ""]
        [(string=? "a" (substring s 0 1))
         (prog2 (substring s 1))]
        [(string<=? "b" (substring s 2))
         (string-append "x" (prog2 (substring s 1)))]
        [else
         (string-append "y" (prog2 (substring s 2)))]))

1. (prog2 "a")
2. (prog2 "ca")
3. (prog2 "abcd")
4. (prog2 "abbbcd")
5. (prog2 "abcdef")

Writing 1

A bubble is poison if its color is green and its x and y coordinate differ by less than 20.

1. Write a program to identify a poison bubble. Use the struct given for the type of a bubble.

   (define-struct b (center radius color))

2. In your bubble wrap game, the model is a list of bubbles. Rewrite the mouse-handler so that when you click on a poison bubble, one additional bubble appears on the screen.