Compilare: user.cpp: In function ‘bool check(std::string)’: user.cpp:11:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0; i<s.size(); i++) ^ user.cpp:20:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (x>=s.size()*2/3) return true; ^