Why does this code give output 0?

Question

int i;
int a[] = {1,2,3,4};
for (i = 0; i< 3; i++)
{ a[3] = a[3] - a[i];}
cout << a[3] - a[i];

First round of for loop:
i = 0, a[3] = 4,
Now a[3] = 4 - 1 = 3
Second round of the loop:
i = 1, a[3] = 3,
Now a[3] = 3 - 2 = 1
Third round:
i = 2, a[3] = 1
Now a[3] = 1 - 3 = -2.

The last cout should give - 2 - 3 = -5

But the output is 0. Where did I get it wrong?

Answer 1

For that, you need to print the output inside loop.
You can see where the curly braces are closed.
In outside loop, it just uses the last value of i which is 3.
So, a[3]- a[i] is same as a[3]-a[3] hence, output is 0.

Answer 2

Thanks!