ITEC 380 2015fall ibarland

most recent semester

hw03
structs
breakout structs

Due:
Section 01: Sep.16 (Tue) 23:59, on D2L and hardcopy in the following class
Section 11: Sep.17 (Wed)18 (Thu) 23:59, D2L.
Your submitted file should be named “hw03.rkt”¹.

Standard instructions for all homeworks:

• Your name, the assignment-number, and the URL of this assignment must be in a comment at the start of the file.
• Any code which results in syntax errors will generally not earn more than 50% of the points-possible. For grading, I will ignore any commented-out code (unless the problem is explicitly asking for commented-out code, ’course).
• If your hardcopy is more than 1page, it must be stapled.
• Format well (in particular, each open-paren should be preceded by a space or start-of-line, for now).

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)

1. 
   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, the final function might get by with fewer tests — perhaps even just one.) You only need turn in your refactored versions.

   You only need steps 4,5,7,8 of the design recipe (once you decide what how you'll represent "size", which is a straightforward choice), and we're only using existing, simple datatypes (so no steps 1-3 or 6).

2. (10pts) Watching a DVD takes longer than just the movie's play time: It takes 5 minutes to get everybody together, 1 minute to start the disc playing, and 3 minutes per preview (G-rated movies have 8 previews, all others have 4). Then, once the movie itself starts, there is a 5-minute pause for a bathroom break after every 42 minutes of movie (so long as the movie is still going).

   Write the function actual-time which takes in a dvd struct (from lecture), and returns the actual time (in minutes) required to watch it.

   hints:

   • The functions quotient and remainder can be helpful.
   • The built-in function zero? can be effected by using (= 0 …) but is still surprisingly handy.
   • You can use let*, or just use if as sub-expression of a larger expression.
   • You get more points for having a test-case that fails than for not having a test case that would fail.

   You only need steps 4-8 of the design recipe, since we already did steps 1-3 of in lecture, for dvds.

3. Familiarize yourself with the Breakout arcade game, such as at kongregate.com. We will write a simplified version which does not need to deal with: score, powerups, having more than one level, or number-of-lives.
   1. (5pts) What are three different types of things (objects) in the game, that our program will need to model?
   2. (5pts) For one of the types in (a) above² give a Java class definition for it (fields and the “natural” constructor³ only). Create two or three instances of the object (presumably in a test method that does nothing else). You'll submit a .java file along with a .rkt file.
   3. (5pts) Repeat the previous step (b), but in racket. (That is, give a struct-definition w/ a comment indicating the field-types, and create at same two examples.) All field-names should correspond directly — e.g. if a Java field was named “numPages”, then the racket name would be “num-pages”.
   Note that we are not writing any functions, so we don't have any check-expects. We are just doing steps 1 and 2 (only) of the design recipe (in both Java and in racket).

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/construct an image of that object on the screen.

• Do NOT include information which never changes (is “invariant”) for a class. For example, if all instances of an object are always the same color, so you wouldn't have a field for the color.

See also scheme-resources—ITEC380 Racket resources.

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©2015, Ian Barland, Radford University Last modified 2015.Sep.28 (Mon)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu