ITEC 380 2013fall ibarland aaray

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hw02
handling simple and range data

Due Sep.13 (Fri)15 (Sun) 23:59 (both hardcopy, and on Desire2Learn).
Your name and the assignment-number must be in a comment at the start of the file. Your hardcopy must be stapled.

Use the Beginning Student language¹ All pertinent steps of the design-recipe must be evident; in particular test cases that precede the function are worth a signification portion of the points.

Rather than repeating code, you should have helper functions as appropriate.

1. (10pts) Write the three functions f2c (convert temperatures from °F to °C), c2k (convert °C to K), and f2k (convert °F to K). Include at least 2 test cases for each function.
   For any test cases involving inexact numbers, use check-within with a third argument (tolerance) of 0.000001 or so. (E.g. (check-within (sqrt 2) 1.414 0.001))

   TODO for prof:Ian: the following paragraphs are more about c2f, not f2c!

   

   In some odd countries (namely Canada, and most of the rest of the world), temperatures are measured in degrees Celcius, instead of degrees Fahrenheit. So when you are traveling and you look in the newspaper and see a forecast for 25°C, it might sound chilly until a friendly Canadian citizen tells you that this is a balmy 77°F. Other notable temperatures² include freezing (0°C, which is 32°F), and boiling (100°C, which is 212°F). (However: if you really want to internalize metric, you're better off thinking in terms of new reference points than converting.) The general case for converting degrees-Celcius into degrees-Fahrenheit is given by the arithmetic formula

   F(C) = ⁹⁄₅ · C + 32

   You read in a science article that the surface of the sun is 5700K (“kelvins”³), and that absolute zero is (conveniently) 0 Kelvin. These numbers seem even more baffling, until that same cheerful Canadian tells you that to convert a temperature from Kelvins to °C, you simply subtract 273.15.
   So 0 K (absolute zero) is -273.15°C, which in turn is -459.67°F, brr.
   Similarly, 273.15K (freezing) is 0°C which (as we've seen earlier) is 32°F.

   (Hint: If somebody gives you a temperature in Kelvins, converting that temperature into degrees Celsius is pretty easy. How can you then leverage code from the preceding problem, to convert that many degrees Celsius amount into degrees Fahrenheit?)

   From Futurama The Series Has Landed:

   Fry: Ooh, nighttime on the moon!
   Old coot: It git down to minus one hundr'd, sev'nty-three.
   Fry, worriedly: Fahrenheit, or Celsius?
   Old coot: First one, then th' other.

2. (6pts) Write the function has-suffix?, which determines if one string ends in another.
   Hint: you can use a conditional if you want, but you can also write it using and and no conditional.
3. (6pts) Write the function pluralize, which passes the following tests:

   (check-expect (pluralize 3 "t-shirt") "3 t-shirts") (check-expect (pluralize 1 "fish") "1 fish") (check-expect (pluralize 2 "fish") "1 fishes") (check-expect (pluralize 2 "cactus") "2 cacti")

   You need only specially-handle words ending in “sh” and “us”; to all others you can just form the plural by adding an "s".
   (You definitely need at least one or two more tests. What important input(s) are entirely untested?)

Images in racket

To experiment with functions-which-create-and-handle-images in DrRacket, include (require 2htdp/image) near the top of your file. Then you should be be able to evaluate each of the following:

(rectangle 80 20 'solid 'blue)
(circle 20 'solid 'red)
(ellipse 80 20 'outline 'orange)

(beside (rectangle 80 20 'outline 'blue)
        (circle 20 'solid 'red))
(underlay (rectangle 80 20 'outline 'blue)
         (circle 20 'solid 'red))
; Think of 'underlay' and 'beside' as being "addition for images"

; underlay with an offset:
(underlay/offset (rectangle 80 20 'outline 'blue)
                0
                10
                (circle 20 'solid 'red))


; If you want to explore documentation:
;   In DrRacket, position the caret on a function-name
;   like 'underlay', and hit F1.

Test cases for images

For functions that return an image, your expected-value should either be (a) an expression involving calls to: the image primitives and/or previously-tested functions, OR (b) an image-literal (but, show the expressions you used to create that image-literal).

For example, if the problem were to "create a function that takes in a width, and returns a solid purple rectangle with the given width and a 16:9 aspect ratio", then the "expected result" part of the test cases might involve calling the image-library's functions like rectangle:

(check-expect (screen 32) (rectangle 32 18 'solid 'purple))
(check-expect (screen 16) (rectangle 16 9 'solid 'purple))
(check-expect (screen 0) (rectangle 0 0 'solid 'purple))
  ; Note: for the expected 0x0 rectangle, I could equally well write:
(check-expect (screen 0) empty-image)

4. 
   1. (3pts) Write a function which takes in a size, and returns an image of a brown donut. (Mmmm, doughnut.)
   2. (3pts) Write a function eyes which takes a size and a color, and returns two colored rings side-by-side.
   3. (4pts) As needed, refactor the above functions so that there is little-to-no repeated code. (If the underlying helper function has a solid set of tests, then fewer -- perhaps even just one -- test cases can suffice for the function.)



5. (3pts) Write a function chomper which takes in a number in [0,1], an returns a pac-man-esque figure whose mouth is the open the indicated fraction. That is, (chomper 0.9) would return an image of a pac-man-esque figure whose mouth is nearly as wide-open as it will ever be.

   Alas, the library 2htdp/image doesn't contain any function for drawing arcs of circles/discs. If you would like such a function, download the file arc.rkt and save it to⁴ the same directory as your program. Then, in your program, include the line (require "arc.rkt")⁵. This will allow you to call ellipse/arc, which is similar to ellipse but with a start/stop angle: (Alternately, a more crude way of making a mouth is by overlaying a triangle onto a circle; this has the drawback that it obscures anything drawn behind the "open" mouth.)

6. (5pts) Familiarize yourself with the Pac-Man arcade game, such as at kongregate.com. Focusing just on the main character (not the rest of the board/game):
   What fields does a pac-man structure (object) have? For each, give
   1. a descriptive one-word field name,
   2. the type you'd use to represent it,
   and
   3. a short explanation/comment (one sentence or less).
   (I expect most answers will have 4 to 7 fields.)

   Hints:

   • Imagine a friend has two different snap-shots of the game; what is the minimal information that your friend needs to tell you so that you can always properly draw the image of the pac-man on the screen?

   • Do not include information that is not part of the Pac-Man itself. For example, the location of the walls is not part of the Pac-Man.

   • Do NOT include information which never changes (is “invariant”). For example, the fact that the pac-man is yellow never changes, so you wouldn't have a field for the color.

See also scheme-resources—ITEC380 Racket resources.

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©2013, Ian Barland, Radford University Last modified 2013.Oct.04 (Fri)

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