You are initializing i with itself. The both i's in int i = i; are the inner one not the outer one. This is undefined behavior and you may get 0 or anything may happen.
This is the right way if you want to assign the outer i to the inner i.
#include <iostream>
int i = 1;
int main()
{
int i = ::i;
std::cout << "i: " << i << "\n";
return 0;
}
Live Demo
BTW, You should carefully read all the compiler warnings. If you did you could see the problem yourself:
warning 'i' is used uninitialized in this function
