The break and continue keywords
Inside the body of any of the looping
constructs while, do-while, or for, you can control
the flow of the loop using break and
continue. break quits the loop without
executing the rest of the statements in the loop. continue stops the
execution of the current iteration and goes back to the beginning of the loop to
begin a new iteration.
As an example of break and
continue, this program is a very simple menu system:
//: C03:Menu.cpp
// Simple menu program demonstrating
// the use of "break" and "continue"
#include <iostream>
using namespace std;
int main() {
char c; // To hold response
while(true) {
cout << "MAIN MENU:" << endl;
cout << "l: left, r: right, q: quit -> ";
cin >> c;
if(c == 'q')
break; // Out of "while(1)"
if(c == 'l') {
cout << "LEFT MENU:" << endl;
cout << "select a or b: ";
cin >> c;
if(c == 'a') {
cout << "you chose 'a'" << endl;
continue; // Back to main menu
}
if(c == 'b') {
cout << "you chose 'b'" << endl;
continue; // Back to main menu
}
else {
cout << "you didn't choose a or b!"
<< endl;
continue; // Back to main menu
}
}
if(c == 'r') {
cout << "RIGHT MENU:" << endl;
cout << "select c or d: ";
cin >> c;
if(c == 'c') {
cout << "you chose 'c'" << endl;
continue; // Back to main menu
}
if(c == 'd') {
cout << "you chose 'd'" << endl;
continue; // Back to main menu
}
else {
cout << "you didn't choose c or d!"
<< endl;
continue; // Back to main menu
}
}
cout << "you must type l or r or q!" << endl;
}
cout << "quitting menu..." << endl;
} ///:~
If the user selects ‘q’ in
the main menu, the break keyword is used to quit, otherwise the program
just continues to execute indefinitely. After each of the sub-menu selections,
the continue keyword is used to pop back up to the beginning of the while
loop.
The while(true) statement is the
equivalent of saying “do this loop forever.” The break
statement allows you to break out of this infinite while loop when the user
types a ‘q.’
