CONTROL STRUCTURES II: REPETITION - Java Programming: From Problem Analysis to Program Design - page 255

The next few sections describe the various forms of while loops.

Counter-Controlled while Loops
Suppose you know exactly how many times certain statements need to be executed. For
example, suppose you know exactly how many pieces of data (or entries) need to be read. In
such cases, the while loop assumes the form of a counter-controlled while loop. (If you
know the number of iterations in advance, a for loop should be used.) Suppose that a set of
statements needs to be executed N times. You can set up a counter (initialized to 0 before the
while statement) to track how many items have been read. Before executing the body of the
while statement, the counter is compared with N .If counter < N , the body of the while
statement executes. The body of the loop continues to execute until the value of counter >=
N . Thus, inside the body of the while statement, the value of counter increments after it
reads a new item. In this case, the while loop might look like the following:

5

counter = 0; //initialize the loop control variable

while (counter < N) //test the loop control variable
{

.
.
.
counter++;

//update the loop control variable

.
.
.

}
If N represents the number of data items in a file, then the value of N can be determined
several ways: The program can prompt you to specify the number of items in the file; an
input statement can read the value; or you can specify the first item in the file as the number
of items in the file, so that you need not remember the number of input values (items). This
is useful if someone other than the programmer enters the data. Consider Example 5-3.

EXAMPLE 5-3

Suppose the input is:
8 9 2 3 90 38 56 8 23 89 7 2
Suppose you want to add these numbers and find their average. Consider the following
program.
//Counter-controlled while loop

import java.util.*;

public class CounterControlledWhileLoop
{

static Scanner console = new Scanner(System.in);