The following C++ program aims to calculate the sum of some ints at compile time:

//BEGINS SUM.CPP
template<int N>
class Sum { 
public:
    enum { val = N };
    template<int K>
    class Inc : public Sum<val + K> { };
};

int main() {
  return(Sum<2>::Inc<3>::Inc<6>::Inc<4>::val);
}
//ENDS SUM.CPP

Now GCC produces:

$ g++ sum.c
$ ./a.out ; echo $? 
6

More generally, every Sum<x_0>::Inc<x_1>::Inc<x_2>::...::Inc<x_n>::val is always expanded to just x_0 + x_n. When compiled with Digital Mars C++ the same example produces 15 as output (more generally, produces the sum of all the provided integers as I would expect). 
Which is the right behaviour?

---
$ g++ -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ./gcc-4.3.3/configure
Thread model: posix
gcc version 4.3.3 (GCC)

I checked this example against a barebone, fresh 4.3.3 build with just gcc-core and gcc-g++, gmp-4.2.1 and mpfr-2.3.0, all downloaded from a gcc mirror, fully boostrapped with no options on a Gentoo distribuition. The same behaviour occurs with a 4.1.2 GCC version on Gentoo and with a 3.4.4 GCC version on Cygwin. The Digital Mars C++ compiler version I used is 8.50 for win32.