BOOK NOTES
CHAPTER 7

7.1 WHILE LOOPS

- repeatedly execute one or more statements
- while statement/loop
  - syntax
    while (<condition>)
        statement
    - statement is usually a block statement
    - statement is executed as long as the condition is true
- flowchart
- infinite loop
  - program never stops
  - exit from containing method
  - commonly caused by 
    - forgetting to update variable tested in the condition
    - updating the variable incorrectly
- off-by-one errors
  - solve by thinking through simple test cases
  - think about what each variable is supposed to represent 
    through time
- do loop
  - perform the body of the loop at least once
  - syntax
    do
        statement
    while (condition);
  - flowchart
  - not as common
  - can always be implemented as a while loop
- spaghetti code
  - possible to draw flowcharts that can't be programmed
    with loops
  - goto statements and corresponding labels
  - extremely hard to read and understand
  - modern programmers rarely use
  - not supported in Java

7.2 FOR LOOPS

- common loop type
  i = start;
  while (i <= end) {
      ...
      i++;
  }
- special form
  for (i = 0; i <= end; i++) {
      ...
  }
- declare the loop counter variable inside the for loop 
  header
  for (int i = 0; i <= end; i++) {
      ...
  }
  - restricts usage to within loop
- general syntax
  for (initialization; condition; update)
      statement
- use when a variable runs from a starting to an ending 
  value with a constant increment or decrement
- flowchart
- slots may contain any expressions
- bad taste to put expressions unrelated to conditions
- should only initialize, test, and update a single variable
- idiom for a while loop of a particular form; only use for 
  this purpose
- if run a loop without a body
  - must follow with an "empty statement" terminated by a 
    semi-colon
  - place in a line by itself to make it stand out
  - don't place a semicolon after the for loop header, or it 
    will act like this
- 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
- scope of variables defined in a for loop header
  - if need to use outside of the loop, must declare outside 
    of the loop
  - can put multiple statements in each expression of the 
    header by separating them with commas
    - less confusing to only have one control variable in 
      the header

7.3 NESTED LOOPS

- e.g. printing a table with rows and columns
- body of a loop is another loop

7.4 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
- implementing loops
  - list the work that needs to be done in every step of the 
    loop body
  - find out how often the loop is repeated
    - for loop is usually appropriate if loop is executed a 
      definite number of times
    - while loop if don't know how many times body will be 
      repeated
  - for a while loop, find out where you can determine that 
    the loop is finished
    - before
      - may never be executed
      - while(condition)
    - middle: loop and a half
    - end
      - always executes at least once
      - do/while loop
  - put operation into body
    - for loop usually uses index
  - double check variable initializations
  - check for off-by-one errors
    - consider the simplest possible scenarios
    - verify results if 
      - never executed 
      - executed exactly once
- symmetric and asymmetric 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
    - i = a; i <= b
    - executed b - a + 1 times
    - fence post error: fence with 10 sections has 11 posts
  - increment other than one
    - symmetric: (b - a) / c
    - asymmetric: (b - a) / c + 1
- loop and a half problem
  - combine assignment and test in loop condition
    - expression with a side-effect
    - generally bad style because hard to read and maintain
  - exit the loop in the middle
    - return statement
    - break statement
- break and continue statements
  - break
    - exit a loop
    - generally a poor way of exiting a loop
    - cannot be used to exit an if statement
    - difficult to use correctness proof techniques
    - some programmers find it useful for loop and a half
    - break label;
      - break out of a nested statement
      - jump to the end of the statement tagged with label
      - tag statement with label
        - syntax:
          label: statement
      - recommended use additional methods instead of 
        complicated nested loops
  - continue
    - jump to the end of the current iteration of the loop
    - rarely used

7.5 RANDOM NUMBERS AND SIMULATIONS

- simulation
  - generate events
  - evaluate outcome
  - randomized in book
- random number generator
- Random class
  - nextInt(n): 0 <= retval < n
  - nextDouble(): 0 <= retval < 1
  - actually pseudorandom