5.5.1. The break Statement

A break statement terminates the nearest enclosing while, do while, for, or switch statement. Execution resumes at the statement immediately following the terminated statement.

A break can appear only within an iteration statement or switch statement (including inside statements or blocks nested inside such loops). A break affects only the nearest enclosing loop or switch:

string buf;
while (cin >> buf && !buf.empty()) {
    switch(buf[0]) {
    case '-':
        // process up to the first blank
        for (auto it = buf.begin()+1; it != buf.end(); ++it) {
              if (*it == ' ')
                   break; // #1, leaves the for loop
              // . . .
        }
        // break #1 transfers control here
        // remaining '-' processing:
        break; // #2, leaves the switch statement

    case '+':
        // . . .
    } // end switch
   // end of switch: break #2 transfers control here
} // end while

The break labeled #1 terminates the for loop that follows the hyphen case label. It does not terminate the enclosing switch statement and in fact does not even terminate the processing for the current case. Processing continues with the first statement following the for, which might be additional code to handle a hyphen or the break that completes that section.

The break labeled #2 terminates the switch but does not terminate the enclosing while loop. Processing continues after that break by executing the condition in the while.