LECTURE NOTES
CHAPTER 7

REPETITION

- repeatedly execute one or more statements

WHILE LOOP

while (<condition>)
    <statement>

- executes statement as long as condition is true
- flowchart
- statement can be a block statement

- examples:

while (!gameOver()) {
    currentPlayer.takeTurn();
    if (currentPlayer == redPlayer) {
        currentPlayer = blackPlayer;
    } else {
        currentPlayer = redPlayer;
    }
}

DO LOOP

do
    <statement>
while (<condition>);

- perform the body of the loop at least once
- flowchart
- not as common
- can always be implemented as a while loop

do
    System.out.println("Please enter an integer: ");
while (!stdin.hasNextInt());

FOR LOOP

int i = 0;
while (i < 5) {
    System.out.print("i = " + i);
    i++;
}

for (<initialization>; <condition>; <update>)
    <statement>

for (int i = 0; i < 5; i++) {
    System.out.println("i = " + i);
}

- initialize, test, and update a single variable
- use when a variable runs from a starting to an ending 
  value with a constant increment or decrement
- flowchart
- scope of variables defined in a for loop header limited to
  within loop
  - if need to use outside of the loop, must declare outside 
    of the loop

PROGRAMMING WITH LOOPS

- infinite loop
  - program never stops
  - exit from containing method
  - commonly caused by 
    - forgetting to update variable tested in the condition
    - updating the variable incorrectly

for (int i = 1; i != 10; i++) {
    System.out.println(i);
    i++;
}

- off-by-one errors
  - solve by thinking through simple test cases
  - think about what each variable is supposed to represent 
    through time

- don't use != to test the end of a range, because it 
  assumes something about the beginning of the range or the 
  increment that may not be correct

NESTED LOOPS

- body of a loop is another loop

- NestedLoops.java

PROCESSING SENTINEL VALUES

- sentinel value
  - used to indicate the end of a data set
  - not part of the data
  - be careful to choose something that couldn't be a real 
    value
- loop and a half
  - if termination condition can only be evaluated in the 
    middle of a loop, use a boolean flag to control that loop

boolean done = false;
while (!done) {
    System.out.println("Input something: ");
    String input = stdin.nextLine();
    if (input.equalsIgnoreCase("quit")) {
        done = true;
    } else {
        System.out.println(input);
    }
}

LOOP BOUNDS

- symmetric bounds: equality on both sides
- asymmetric bounds: one side equal but other side not
- don't force symmetric

- determine bounds
  - count iterations
  - easier with asymmetric bounds
    - i = a; i < b
    - executed b - a times
  - symmetric bounds
    - fence post error: fence with 10 sections has 11 posts
    - i = a; i <= b
    - executed b - a + 1 times
  - increment other than one
    - asymmetric: (b - a) / c
    - symmetric: (b - a) / c + 1

SIMULATIONS

- generate events
- evaluate outcome
- frequently need randomized

RANDOM

- java.util.Random
  - pseudorandom number generator
  - methods
  - int nextInt(int n): 0 <= retval < n
  - double nextDouble(): 0 <= retval < 1