Compilare: user.cpp: In function ‘std::ifstream& operator>>(std::ifstream&, cost_matrix&)’: user.cpp:16:16: warning: no return statement in function returning non-void [-Wreturn-type] f >> x; } } } ^ user.cpp: In member function ‘long long int& even_mat::la(int, int)’: user.cpp:27:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] else if((b-a+1)/2-1 >= buf[a].size()){ ^ user.cpp: In function ‘long long int calc_cost(const string&, const cost_matrix&)’: user.cpp:33:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i+1 < str.size(); ++i){ ^ user.cpp:35:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int dist = 4; dist <= str.size(); dist += 2){ ^ user.cpp:36:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0, j = dist-1; j < str.size(); ++j){ ^