1+2+3+...+n

#include <iostream>

using namespace std;

template<int N>
struct CalCls
{
    enum {sum = CalCls<N-1>::sum + N};
};

template<>
struct CalCls<0>
{    
    enum {sum = 0};
};


int main()
{
    cout<<"1+2+3+...+100 = "<<CalCls<100>::sum<<endl;
    return 0;
}