READING
Chapter 6
Section 1
"The while Statement"

- repetition statement
  - type of control statement
  - repeatedly execute a block of code
  - aka loop statement
- recursive method
  - method that calls itself
  - alternative to repetition
- while statement
  - syntax
    while ( <boolean expression> )
    
        <statement>
    - <statement>
      - <single statement> or <compound statement>
        - compound statement requires braces
      - aka loop body
  - loop body is executed as long as the boolean expression is true
  - diagram
    - diamond for loop condition
    - rectangle for loop body
    - arrow into diamond
    - true arrow from diamond to rectangle
    - arrow from rectangle to above diamond
    - false arrow out of diamond
- count-controlled loop
  - execute loop body a fixed number of times
- repetition control to improve the user interface
  - previously assumed the input was valid
  - more user friendly to handle invalid input
  - selection statement limitations
    - only allows one alternative
    - e.g. printing an error message
    - better to allow the user to re-enter the value until it is correct
- priming read: reading of a value before the testing is done
- sentinel-controlled loop: loop body is executed repeatedly until any one of the designated values (sentinel) is encountered
- +=

Quick Check
1. int curNum = 11;
   int sum = 0;
   while (curNum <= 20) {
       sum = sum + curNum;
       curNum++;
   }
   This is a count-controlled loop.
2. String strEntered = JOptionPane.showInputDialog("Enter a real number:");
   double dEntered = Double.parseDouble(strEntered);
   while (dEntered >= 0) {
       strEntered = JOptionPane.showInputDialog("Enter a different number:");
       dEntered = Double.parseDouble(strEntered);
   }
3. Change the while loop to:
   while (sleepHour != 0) {
       if (sleepHour > 0) {
           sum += sleepHour;
           cnt++;

           sleepHour = getDouble("Enter sleep hours (0 - to stop:");
       }
   }