Compilare: user.cpp: In function ‘int main()’: user.cpp:14:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<c.length();++i) ~^~~~~~~~~~~ user.cpp:21:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<(*it).second.size();++i) ~^~~~~~~~~~~~~~~~~~~~