What does while mean in computer programming?

Answer 1

The while() statement is used in iterative structures (loops), such that a statement block will iterate so long as a conditional expression evaluates true. The conditional expression can be evaluated at the start or at the end of a loop, thus making it more flexible than the standard for() statement which always evaluates the conditional expression at the start of a loop.

In C++, the while() statement has the following forms:

while( condition ) {

statement;

}

do {

statement;

} while( condition );

In the first form, the statement block only iterates if the condition evaluates true. In the second form, the statement block is executed at least once, and only iterates if the condition evaluates true.

Infinite loops have the following forms:

while( 1 ) {

statement;

}

do { statement;

} while( 1 );

The latter form is redundant since both loops will iterate at least once, however the former is deemed more acceptable in terms of readability than the infinite for() statement:

for(;;) {

statement;

}

As with for() statements, while() loops can use break, return or goto to conditionally exit the loop at any point, or use continue to prematurely begin a new iteration.

Although for() and while() are interchangeable to an extent, the form you use is largely dependant upon which is more readable or makes the most sense in your code. If the condition must be evaluated at the end of the loop then you must use do..while(), but for all other loops you often have a choice of using for() or while(). However, there are differences. Generally speaking, for() statements are used whenever you need to operate upon a control variable in a consistent manner (such as incrementing an index value at each iteration) whereas while() statements are used when changes to the control variable are dependant upon other conditions which are determined within each iteration of the loop itself. Moreover, control variables in while() loops must be in scope prior to entering the loop and will remain in scope when the loop terminates, whereas for() loops can both declare and initialise control variables, rendering them local to the loop. Depending on the type of loop, these facts can help determine which is the better form to use, but in terms of performance there is no real difference. It's all a question of which form makes the most sense for the type of loop you are trying to control.