How the answer of this for loop is 5?

Question

I was practicing my C skills online. And I got a question like:

What is the output of this program?

void main(){
int i;
for(i=1;i++<=1;i++)
i++;
printf("%d",i);
}

The answer was 5. But I thought the for loop would execute endlessly. As the i will be incremented on each iteration and i will be never less than or equal to 1. how come 5 will be the output of this program?

Answer 1

This is explained by the sequence of events:

i = 1; // for init
i++ <= 1 ? true // for condition, i evaluates as 1 but is made into i = 2 after the expression
i++; // inside for body, makes i = 3
i++; // for increment, makes i = 4
i++ <= 1 ? false // for condition again, i evaluates as 4 but is made into i = 5 after the expression
// condition is false, for loop ends, i = 5

Perhaps you are forgetting that the for condition, although false, is still executed to verify that before the program decides the loop is terminated.