While loop go into infinite loop when 0,1

Question

Why this code does not print awesome

#include <iostream>
using namespace std;
int main() {
    while (1, 0) {
        cout << "awesome\n";
    }
    return 0;
}

But this code prints awesome Infinite times

#include <iostream>
using namespace std;
int main() {
    while (0, 1) {
        cout << "awesome\n";
    }
    return 0;
}

I'm using g++ compiler

aperture_dev · Answer 1 · 2017-03-06T15:45:53.630

2

because the while loop doesn't care about the first part of your expression.

#include<iostream>
   using namespace std;

int main(){
   while(0 <- ,1){cout<<"awesome\n";}
   return 0;
}

This part will be ignored. Compile your code with -Wall.

If this part will be ignored, the code is false in the first example and true in the last example.

edited Mar 06 '17 at 15:45

answered Mar 06 '17 at 12:54

aperture_dev

39
3

1

it does care about the first part, it just doesn't use the result. If you had an int and incremented it here, it would work – Asoub Mar 06 '17 at 15:30
Yes, you're right. But the while-expression does not care about it. – aperture_dev Mar 06 '17 at 15:45

score 1 · Answer 2 · edited May 23 '17 at 11:46

1

Because you're using the comma operator (Does while loop have two Arguments?) which evaluates the first operand (before comma) and returns the second.

Which means that in your first loop, you're doing while(0), and 0 is evaluated to false (immediatly ends). And in your second your doing while(1), and 1 is evaluated to true (infinite loop).

edited May 23 '17 at 11:46

Community

1
1

answered Mar 06 '17 at 12:53

Asoub

2,273
1
20
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While loop go into infinite loop when 0,1

2 Answers2