I've heard that objective-C is a proper superset of C, but is objective-C 2.0?

The reason I ask is that either it isn't, or I misunderstand the phrase 'proper superset', because this code is valid C syntax:

import

int main () {
    char *nil = "hello";
    printf("%s\n",nil);
}

But does not compile in Objective-C 2.0. Obviously, this is an easily fixable problem, but I'm writing a paper, and feel that this is something that should be pointed out.