Decrementing the Loop Control Variable

The loop control variable in a counting loop can be changed by a negative value. Here is a program fragment that decrements the loop control variable at the bottom of each iteration:

    int count = 2;                 // count is initialized
    while ( count >= 0 )           // count is tested
    {
      System.out.println( "count is:" + count );
      count = count - 1;           // count is changed by -1
    }
    System.out.println( "Done counting down." );      

Here is what the program will print:

count is: 2
count is: 1
count is: 0
Done counting down.

Here is what happens, step-by-tedious-step:

1. count is initialized to 2.
2. The condition, count >= 0 is evaluated, yielding TRUE.
3. The loop body is executed, printing "count is: 2" and subtracting 1 from count.
   • count is now 1.
4. The condition, count >= 0 is evaluated, yielding TRUE.
5. The loop body is executed, printing "count is: 1" and subtracting 1 from count.
   • count is now 0.
6. The condition, count >= 0 is evaluated, yielding TRUE.
7. The loop body is executed, printing "count is: 0" and subtracting 1 from count.
   • count is now -1.
8. The condition, count >= 0 is evaluated, yielding FALSE.
9. The statement after the loop, is executed, printing "Done counting down."