for(i=0;i<vector.size()-1;++i)

size_t is unsigned integer, so size()-1 is not -1. We should use i+1<vector.size() instead.

• Notes
  • A Functor is a object which acts like a function. Basically, a class which defines operator().
• Refs
  • What are C++ functors and their uses?
  • Functors in C++