Using a variable with the same name in different spaces

Question

This code compiles, but I have a run time error in Visual Studio:

Run-time check failure #3 - the variable 'x' is being used without being initialized...

int x = 15;
int main()
{
    int x = x;
    return 0;
}

I don't understand that behavior... in the error box when I click continue the program resumes and x has a corrupted content (like -8556328 instead of 15).

Why does this code work without a problem, and the int array is well declared?

const int x = 5;
int main()
{
     int x[x] = {1,2,3,4};
     return 0;
}

Answer 1

x is defined at the left of =.

so in x[x], [x] refer to the global one,

whereas in x = x;, x hides the global x and initializes from itself -> UB.

Answer 2

When you declare a new variable, its name becomes visible right here

int x =
//     ^- there

because it is at that point the variable is fully declared, and as such; its name means something. At this point in time any other (previously declared variable) in a surrounding scope will be hidden.

Answer 3

There is no scope resolution operator in C, so you may not be able to use

int x = x;

in your program.