The break keyword is used to break out of a do, for, or while loop. It is also used to finish each clause of a switch statement, keeping the program from "falling through" to the next case in the code. An example:

   while( x < 100 ) {
     if( x < 0 )
       break;
     cout << x << endl;
     x++;
   }            

A given break statement will break out of only the closest loop, no further. If you have a triply-nested for loop, for example, you might want to include extra logic or a goto statement to break out of the loop.