Reason for using non-type template parameter instead of regular parameter?

Question

In C++ you can create templates using a non-type template parameter like this:

template< int I >
void add( int& value )
{
  value += I;
}

int main         


        

Answer 1

There are lots of reasons, like doing template metaprogramming (check Boost.MPL). But there is no need to go that far, C++11's std::tuple has an accessor std::get that needs to be indexed at compile time, since the result is dependent on the index.