Why int main() returns with an value of unsigned char range? [duplicate]

Good night,

Take as example the follow program:

int main()
{
    return 0;
}

Everything works fine and I get the follow message on the console indicating that the program exited with code 0:

hh:mm:ss: /path/to/executable exited with code 0

Now when I try this:

int main()
{
    return -1;
}

I get the same message, except that it says that I exited with code 255:

hh:mm:ss: /path/to/executable exited with code 255 (instead of -1):

Now switching to return 256 it says that the program exited with code 0, which make me think that it should be actually unsigned char main() instead of int main(), since that the return type behaves like a unsigned char type.

Why does that happen?

Thanks in advance.