cloopsfor-loopcompound-assignment

For loop confusion

I have :

#include <stdio.h> 
int main(void) { 
int s,i,t[] = { 0, 1, 2, 3, 4, 5 }; 
s = 1; 
for(i = 2; i < 6 ; i += i + 1) 
s += t[i]; 
printf("%d",s); 
return 0; 
}

Why is the result 8?

What I'm thinking:

first loop: 2<6 True
i+=i+1 is 5
s=1+t[5] =>1+5=6
second loop : 5<6 True
i=5+5+2=11
s=6+t[11]???
Solution

  • I will guide you to the for loop reference:

    iteration-expression is evaluated after the loop body and its result is discarded. After evaluating iteration-expression, control is transferred to cond-expression.

    In your example, i += i + 1, which is the iteration expression we're talking about, is evaluated after the loop body.

    Taking this into account, the result will be 8