IT - While Loops (Lesson)

While Loops

Introduction

Many times, in programming it is necessary to repeat a segment of code multiple times. It would be very tedious to write lines of code repeatedly and it would not be very efficient. Loops allow you to repeat segments of code many times.

while loops are indefinite loops because they do not have a predetermined number of iterations. A while Loop will keep iterating until the boolean condition that it evaluates is false.

while Loops

while (/*boolean expression*/)
{
//body
}

Within the body, there needs to be something that would cause the boolean expression to become false or the result would be an infinite loop. An infinite loop is a loop that keeps going forever.

Predict the output of the following loop:

int i = 9;
while (i < 18)
{
System.out.print (i + " ") ;
i += 2;
}

Output:

9 11 13 15 17

Sentinel Value

Some while loops will contain a sentinel value. The sentinel value, often -1 or -999, is a value that a user can enter to stop the loop. For example, if you were creating a program where users were entering student grades, the program might ask users to enter -1 when they were finished. The boolean expression would be looking for a grade that was obviously greater than or equal to zero so a negative value would stop the loop.

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