How's the output is 2

Question

int a[3] = { 9, 3, 4 };
for (int i = 2; i > 0; i--) {
a[0] -= a[i];
}
cout << a[0];

Answer 1

thanks for helping me bro @swim

Answer 2

the statement a[0] - =a[i] will be executed every time till the for loop run?

Answer 3

Man i am so dumb I'm literally learning this sh*t from days.. yet can't figure it out..