6.6 break Statement

We have used a while statement to compute Fibonacci numbers less than 100. The loop exits when the condition at the beginning becomes false. Loops also can be exited at any point through the use of a break statement.

Suppose you want to add a series of numbers and you don't know how many numbers are to be added together. You want to read numbers and need some way of letting the program know it has reached the end of the list. Example 6-2 allows you to use the number zero (0) to signal the end of the list.

Note that the while statement begins with:

while (true) { 

The program will loop forever because the while would exit only when the expression true is false. The only way to exit this loop is through a break statement.

We detect the end-of-list indicator (zero) with the statement following if statement, then use break to exit the loop.

if (item == 0) 
     break;  

Example 6-2. total/total.cpp

#include <iostream>

int   total;  // Running total of all numbers so far
int   item;   // next item to add to the list 

int main(  )
{
    total = 0;
    while (true) {
        std::cout << "Enter # to add \n";
        std::cout << "  or 0 to stop:";
        std::cin >> item;

        if (item == 0)
            break;

        total += item;
        std::cout << "Total: " << total << '\n';
    }
    std::cout << "Final total " << total << '\n';
    return (0);
}

Note that this program makes use of an old programming trick called an indicator to end the input. In this example, our end-of-input indicator is the number 0.