factorial with C++ templates

factorial.cpp

#include <iostream>

template<unsigned long M>
struct f
{
  static const unsigned long value = M * f<M-1>::value;
};

template<>
struct f<0>
{
  static const unsigned long value = 1UL;
};

int
main ()
{
  std::cout << f<0>::value << std::endl;
  std::cout << f<3>::value << std::endl;

  char a[f<10>::value];

  std::cout << sizeof (a) << std::endl;
}