Why doesn't the C++11 compiler complain when I initialize a local variable with the same name multiple times within the same scope?

So if I initialize a variable of the same type and name within the main function the compiler will complain of the re declaration, for example:

for (int i = 0; i < 5; i++)
{
    int a{5};
    int a{5}; // error int a previously declared here
}

But there are no errors if I compile this instead:

for (int i = 0; i < 5; i++)
{
    int a{5};
}

To my understanding, this looks as if I have initialized "int a" multiple times within the same scope which obviously would cause an error. If somebody could explain what's actually happening it would be greatly appreciated! Thanks!