The Do Statement

3. Bottom-driven Loop



Bottom-driven Loop

All loops must do three things:

  1. The loop must be initialized correctly.
  2. The ending condition must be tested correctly.
  3. The body of the loop must change the condition that is tested.

The code fragment includes all three, but in a different order than usual. The ending condition test is done after the loop body has executed.

int count = 0;                       // initialize count to 0

  System.out.println( count );      // loop body: includes code to
  count++  ;                        // change the count
while ( count < 10 );               // test if the loop body should be
                                    // executed again.         

Loops with the test at the top of the loop (while and for loops) are called top-driven loops.

Loops implemented with the test at the bottom (a do loop) are called bottom-driven loops. This location for the test has some odd (and sometimes undesirable) effects. Examine the following:

int count = 1000;

  System.out.println( count );
  count++  ;                  
while ( count < 10 );

Question 3:

What is the output of the revised loop?