Compilare: user.cpp: In member function ‘void Matching::make_matching()’: user.cpp:132:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i <= used -> size(); ++i) ^ user.cpp: In member function ‘void Matching::make_matching_size()’: user.cpp:153:51: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < left_to_right -> size(); ++i) ^ user.cpp: In function ‘int main()’: user.cpp:220:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < left -> size(); ++i) ^