Compilare: user.cpp: In function ‘bool verif(std::__cxx11::string)’: user.cpp:17:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();i++) ^ user.cpp:23:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size()&&r==1;i++) ^ user.cpp: In function ‘int main()’: user.cpp:42:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<s.size();i++) ^