Class 19: More Discussion of Exam 1

Held Tuesday, September 26, 2000

Summary

Today we continue our discussion of exam 1 by visiting the latter parts of the exam.

Notes

• Exam 1 returned.
  • Please don't discuss your grades with others; you should decide whether or not you're satisfied with your work on the basis of your work alone.
  • I've asked some of you to come see me about questions on your exam. Please do so ASAP.
  • You may also see me if I didn't include a note to that effect.
  • Today, we're going to continue to discuss the exam, particularly part C, since there was some confusion.
  • I'll get notes on Part C posted on the Web later this week.
• Are there questions on phase 2 of the project?
• I've decided that I will not be grading homework 1. At this point, I think you've gotten everything you would have out of that assignment.
• Homework 3 is almost ready.

Overview

• Proper citation
• A GCD algorithm in Java
• Orderings and more

Citations

• All works should have an author and a publisher.
  • If you can't determine the author, use Anonymous or the publisher (whichever seems more appropriate).
  • If you can't determine the publisher, incldue a note to that effect.
• Because Web pages change, you need to include additional information.
  • Date visited.
  • Date last modified.

GCD

• Recursive

  public static void gcd(int x, int y) {
    // The GCD of anything and 0 is that thing
    if (x == 0) 
      return y;
    // The GCD of anything and 0 is that thing
    else if (y == 0)
      return x;
    // If y evenly divides x then y is the GCD of x and y
    else if ((x % y) == 0)
      return y;
    else
      return gcd(y, x%y);
  } // gcd(int,int)
  

• Iterative

  public static void gcd(int x, int y) {
    if (x == 0) 
      return y;
    if (y == 0)
      return x;
    int smaller = y;
    int larger = x;
    int tmp;
    while ((tmp = larger % smaller) != 0) {
      larger = smaller;
      smaller = tmp;
    } // gcd(int,int)
  

• Most of you got 8 and 9.
• Any questions?

Orderings

• To be held as a discussion.
• One great observation from your exams
  • ``Classes are like nouns, interfaces are like adjectives''
• If you have associated data or an implementation of a method, you need a class. Otherwise, an interface should suffice.