C++ In a Nutshell

Loops

A loop statement allows you to execute a statement multiple times. Two loop statements, for and while, test at the top of the loop. The do statement tests at the bottom, thereby ensuring that the loop body executes at least once. This section describes the loop statements. See Section 4.6 for additional statements that affect or control loop execution.

A loop statement can declare variables in the scope of the loop’s substatement. Every time the loop iterates, it reenters the substatement scope. This means objects that are declared in the substatement (and in the loop’s condition) are created and destroyed with every loop iteration.

while Statements

A while statement repeats a statement while a condition is true. The syntax is:

while (condition ) statement

The condition is evaluated and converted to bool. If the value is true, statement is executed, and the loop repeats. If the value is false, the loop finishes and execution continues with the subsequent statement. Thus, if condition is false the first time it is evaluated, the statement is never executed.

A continue statement in a while loop branches to the top of the loop, and execution continues with the evaluation of condition. A break statement exits immediately.

A while loop is typically used for unbounded iteration, that is, when you don’t know beforehand how many times a loop will iterate. Example 4-5 shows how the while loop can be used to control I/O.

Example 4-5. Controlling I/O with the while loop

#include <algorithm> ...