University of British Columbia CPSC 110 LAB 1

CPSC 110 LAB 1

HtDF Lab

P3
A (much too) simple scheme for pluralizing words in English is to add an
s at the end unless the word already ends in s.

Design a function that consumes a string, and adds s to the end unless
the string already ends in s.

;; String -> String
;; Adds an s to end of given word, unless word already ends in s
(check-expect (pluralize "hello") "hellos")
(check-expect (pluralize "has") "has")
(check-expect (pluralize "") "")




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;(define (pluralize str) "") ;stub




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;(define (pluralize str)




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; (... str)) ;template
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(define (pluralize str)
(if (string=? str "")
""
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(if (string=? "s" (string-ith str (- (string-length str) 1)))
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str
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(string-append str "s"))))

P4
Design a function called nth-char-equal? that consumes two strings
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and a natural and produces true if the strings both have length greater
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than n and have the same character at position n.

Note, the signature for such a function is:
;; String String Natural -> Boolean
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The template for such a function is:
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(define (nth-char-equal? s1 s2 n)
(... s1 s2 n))
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;; String String Natural -> Boolean
;; Produces true if string-length of s1 and s2 are greater than n and have the same character at position
n
(check-expect (nth-char-equal? "hello" "goodbye" 10) false)
(check-expect (nth-char-equal? "hello" "bell" 6) false)
(check-expect (nth-char-equal? "time" "bath" 3) false)
(check-expect (nth-char-equal? "candy" "mandy" 3) true)


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, ;(define (nth-char-equal? s1 s2 n) false) ;stub

;(define (nth-char-equal? s1 s2 n)
; (... s1 s2 n)) ;template

(define (nth-char-equal? s1 s2 n)
(if (> (string-length s1) n)
(if (> (string-length s2) n)
(string=? (substring s1 (- n 1) n) (substring s2 (- n 1) n))
false)
false))


Balloon Lab




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; Balloon popping




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;; CONSTANTS ==========================




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(define WIDTH 500)
(define HEIGHT 500)
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(define MTS (empty-scene WIDTH HEIGHT))

(define BALLOON-COLOUR "red")
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(define POP-IMAGE (overlay (text "POP!" 80 "black")
(radial-star 30 (/ WIDTH 10) (/ WIDTH 2) "solid" "yellow")))
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(define CTR-X (/ WIDTH 2))
(define CTR-Y (/ HEIGHT 2))
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(define SPEED 2)
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(define MAX-SIZE (/ WIDTH 2))

;; DATA DEFINITIONS ============================
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;; Balloon is one of:
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;; - Number[1, MAX-SIZE]
;; - false
;; interp. number is the radius of balloon in screen pixels, false means balloon is popped
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(define B1 1)
(define B2 false)
(define B3 10)
(define B4 MAX-SIZE)

(define (fn-for-balloon b)
(cond [(and (number? b)


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