fact_by_tmpl.cpp

#include <iostream>

template<unsigned long n>
struct Factorial {
    enum {value = n * Factorial<n-1>::value};
};

template<>
struct Factorial<0> {
    enum {value = 1};
};

int main() {
    std::cout << Factorial<5>::value << std::endl;
    std::cout << Factorial<10>::value << std::endl;
    std::cout << Factorial<20>::value << std::endl;

    return 0;
}