Compilare: user.cpp: In function ‘int main()’: user.cpp:20:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0;i < s.length();++i) ~~^~~~~~~~~~~~ user.cpp:27:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0;i < (*it).second.size();++i) ~~^~~~~~~~~~~~~~~~~~~~~