CSC153, Class 34: Loops ("Laaps" in Plan-Speak)

Overview:
* Review of Conditionals
* Reflection on Conditionals
* Overview of Loops
  + While Loops
  + Do Loops
  + For Loops
* Lab

Notes:
* Happy April Fools' Day.
* Exam 2 returned.  Problem 3 not graded because it was wrong.  
  Whoops!
  We may go over string->value at a later date.
* Read X3 (Input, Output, Files, and Exceptions); Focus on 
  Exceptions.
* Start homework 3 (A Raquetball Simulator).

We've looked at a variety of kinds of conditionals and
Boolean procedures
* Lots of kinds of "if"

How might we incorporate Booleans and conditionals in our
Rational class?

* Is object x a rational?  A Builtin Java procedure, 
  instanceof

   if (x instanceof Rational) ...

* Is the Rational equal to ...
  + Another Rational
  + Another object
* All the comparisons
int numerator;
int denominator;
public boolean lessThan(Rational other) {
  return (this.numerator*other.denominator 
            < other.numerator*this.denominator)
} // lessThan(Rational)
(1) Convert to doubles and compare the doubles
  + Potential approximation
(2) If ad < cb then a/b < c/d
  + Potential overflow
* Back to equals
public boolean equals(Rational other) {
  // Two rational numbers are equal if their reduced
  // forms are the same.
  return (this.reduce().numerator() == other.reduce().numerator())
         && (this.reduce().denominator() == other.reduce().denominator());
  // Problem with above strategy: Reducing costs
  // Alternate solution: Cross-multiply.  Cheaper, but overflow
  return (this.numerator*other.denominator 
            == other.numerator*this.denominator)
} // equals(Rational)

public boolean equals(Object other) {
  return (other instanceof Rational) &&
         (this.equals((Rational) other))
    || (other.instanceof Integer) && ...
}

----------------------------------------

On to Loops

Most languages provide at least three kinds of loops

* "Counting loop"
* "While loop": 
  Test
    Holds -> Do "body" and go back to the test
    Doesn't hold -> Exit loop
* "Repeat loop":
  Do something
  Test
    Holds -> Go back to top
    Otherwise -> Exit loop

for(intitialization; test; increment) {
  body;
}
while (test) {
  body
}
do {
  body
} while (test);

The for loop is simply a shorthand for

initialization
while (test) {
  body
  increment
}

Do J5.1 and J5.3