Compilare: user.cpp: In function ‘std::vector<std::basic_string<char> > split(std::string, char)’: user.cpp:12:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ^ user.cpp: In function ‘int main()’: user.cpp:31:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<x.size();i++) ^ user.cpp:34:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<y.size();j++) ^ user.cpp:37:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(l=0;l<y[j].size();l++) ^