Why will this 'for' loop loop (albeit just once)?

Question

int x;
int main() {
for (; x>=0; --x);
return 0;
}

I don't understand the 3rd line.
Why will this 'for' loop execute once? The initial value is not even set...

Answer 1

Solus here "x" is a global variable and all the global variables are by default initialised as 0.

Answer 2

Default value of integer is 0

Answer 3

AteFish not necessarily since the only x in scope by the time the for loop is reached,is the global x.In other words,there is no x declared in main's scope