Compilare: user.cpp: In function ‘int main()’: user.cpp:18:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s.size(); i++) ^ user.cpp:25:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<s.size(); i++) ^ user.cpp:29:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=i+1; j<s.size(); j++) ^