ITEC 380 2015fall ibarland

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hw04b
structs
space invader structs

Due:
Section 01: Sep.28 (Mon) 14:00, on D2L and hardcopy in class
Section 11: Sep.29 (Tue) 23:59, D2L.
Your submitted file should be named “hw04b.rkt”.

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).

1. (This is the completion of hw04a, from D2L.) Consider the following information, which might be part of a sports-simulation.

   A team is:

   • a name (non-empty string), AND
   • an offense rating (real number), AND
   • a defense rating (real number).

   (5pts) Give a data definition (including examples of the data, and the template for any function which processes a team), as per steps 1-3 of the design recipe. Give at least three examples of a team.

   (10pts) We'll say one team is “greater” than another if its offense is higher than the other's defense, and its defense is higher than the other's offense. Write the function team>? to implement this. Follow all the steps of the design recipe¹. As always, be sure to think about enough test-cases to cover the interesting situations (5 of the pts). (In this case, six or seven should suffice, if they each cover a different situation.)

2. Familiarize yourself with the Space Invaders arcade game, such as at kongregate.com. We will write a simplified version which does not need to deal with: score, multiple waves (levels), enemy shots (though I encourage it), sound, different types of enemies, flying saucers, 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 objectclass (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), for only one of the types.

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, 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.27 (Sun)

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