Java Reference
In-Depth Information
The statement in Line 8 stores the next number in the variable number . The statement in
Line 9 updates the value of sum by adding the value of number to the previous value. The
statement in Line 10 increments the value of counter by 1 . The statement in Line 11
outputs the sum of the numbers. The statements in Lines 12 through 15 output either the
average or the text: Line 15: No input .
Note that in this program, in Line 4, sum is initialized to 0 . In Line 9, after storing the
next number in number in Line 8, the program adds the next number to the sum of all
the numbers scanned before the current number. The first number read is added to zero
(because sum is initialized to 0 ), giving the correct sum of the first number. To find the
average, divide sum by counter .If counter is 0 , then dividing by 0 terminates the
program and you get an error message. Therefore, before dividing sum by counter , you
must check whether or not counter is 0 .
Notice that in this program, the statement in Line 5 initializes the LCV counter to 0 .
The expression counter < limit in Line 7 evaluates whether counter is less than
limit . The statement in Line 8 updates the value of counter . Note that in this program,
the while loop can also be written without using the variable number as follows:
while (counter < limit)
{
5
sum = sum + console.nextInt();
counter++;
}
Sentinel-Controlled while Loops
You might not know exactly how many times a set of statements needs to be executed,
but you do know that the statements need to be executed until a special value is met. This
special value is called a sentinel. For example, while processing data, you might not
know how many pieces of data (or entries) need to be read, but you do know that the last
entry is a special value. In such cases, you read the first item before entering the while
statement. If this item does not equal the sentinel, the body of the while statement
executes. The while loop continues to execute as long as the program has not read the
sentinel. Such a while loop is called a sentinel-controlled while loop. In this case, a
while loop might look like the following:
input the first data item into variable //initialize the
//loop control variable
while (variable != sentinel)
//test the loop control variable
{
.
.
.
input a data item into variable
//update the loop
//control variable
}
 
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