Begin with an index value of zero and count upward

(Display Listing 1.)

The value of the index variable is zero the first time it is tested in the conditional clause of the while loop.

As a result of incrementing the index variable at the end of the body of the loop:

The value of index will have been increased by one each time it is tested against the value of limit in the conditional clause of the while loop. 

The loop continues to execute the  body of the loop while the value of index is less than the value of limit.

When the value of index equals limit, the body of the loop is skipped and control transfers to the code following the loop.