Even for the old C it wasn't a superset. There are plenty of legal C programs that aren't legal C++ - if for nothing else, then because C++ has more reserved k

Even for the old C it wasn't a superset. There are plenty of legal C programs that aren't legal C++ - if for nothing else, then because C++ has more reserved keywords which are perfectly legal identifier names in C. E.g. this is legal C but not legal C++: int template = 10;