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Controlling loop


In the last topic, you learned about loops which are used to repeat a certain process some number of times.

What if we can control the way our loop operates.

In C++, we can jump out of the loop or jump to the starting condition of the loop whenever we want. We do this with the help of break and continue statements respectively.

break


break is used to break or terminate a loop whenever we want.

Just type break; after the statement after which you want to break the loop. As simple as that!

Remember, we had also used break statements in switch..case in the previous topic.

Consider an example.

#include <iostream>
int main(){
    using namespace std;
    int n;
    for(n = 1; n <= 5; n++){
         cout << "*" << endl;
         if(n == 2){
             break;
         }
    }
    return 0;
}
Output
*
*

In the first iteration of the loop in the above example, '*' gets printed and the condition ( n == 2 ) is checked. Since the value of n is 1, therefore the condition becomes false and n++ increases the value of 'n' to 2. Again '*' gets printed and since this time the condition of if satisfies, the break statement terminates the loop.

Let's have a look at one more example of break.

#include <iostream>
int main(){
    using namespace std;
    int x;
    for( ; ; ){
        cout << "Enter 0 to stop" << endl;
        cin >> x;
        if (x == 0){
            break;
    	}
    }
    return 0;
}
Output
Enter 0 to stop
3
Enter 0 to stop
32
Enter 0 to stop
23
Enter 0 to stop
0

This is an infinite loop. To terminate this we are using break. If a user enters 0 then the condition of if will get satisfied and the break statement will terminate the loop.

continue


continue statement works similar to break statement. The only difference is that break statement terminates the loop whereas continue statement passes control to the conditional test i.e., where the condition is checked.

In short, it passes control to the nearest conditional test in do...while loop, or the condition of while in while loop, or the condition of for in for statements skipping the rest of the statements in the loop.

#include <iostream>
int main(){
    using namespace std;
    int n = 1;
    while(n < 10){
        if (n == 5){
        n = n + 1;
      	    continue;
        }
        cout << "n = " << n << endl;
        n++;
    }
    return 0;
}
Output
n = 1
n = 2
n = 3
n = 4
n = 6
n = 7
n = 8
n = 9

In the above example, notice that n = 5 is not printed because as the value of 'n' becomes 5, the if condition becomes true and the statements in the body of the if statements get executed. Thus n = n+1 increases the value of 'n' to 6 and continue statement passes the control to the test condition and rest of the statements are not executed ( cout << "n = " << n << endl; n++; - these two statements are not executed when n is 5 ). Then again the iteration starts and the numbers get printed from 6 onwards.

Knowing is not enough, we must apply. Willing is not enough, we must do.
-Bruce Lee

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