Tips on while Loops

• Don't put a semi-colon after the close paren. The following code:

  while (num != -1);
  {
      num = promptForDouble("Enter a number", keyboard);
      System.out.println("You entered " + num);
  }
  

  is an infinite loop if num starts out as something other than -1!

  If num is -1, the logical expression is false, the while ends (because of the semicolon) and then the next statement (the call to promptForDouble()) is executed once, as is the print statement.

• Here is the while loop with the proper indentation:

while (num != -1)
    ;

num = promptForDouble("Enter a number", keyboard);
System.out.println("You entered " + num);

• A break statement causes execution to jump to the next statement after the loop.

  A continue statement causes execution to jump to the beginning of the loop and re-evaluate the logical condition.

  For instance, you could write the following code

  ...
  while (true)
  {
      quiz = promptForDouble("Please enter a quiz score (-1 to end): ";
      
      if (quiz == -1)
          break;
      if (quiz < 0)
      {
          System.out.println("You must enter a positive quiz score or -1 to end.");
          continue;
      }
      points = points + quiz;
      num = num + 1;
  }
  average = points / num;
  

  Is this a sentinel while loop?