Compilare: user.cpp:11:6: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] main() ^ user.cpp: In function ‘int main()’: user.cpp:17:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i){ ^ user.cpp:18:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j=0;j<s[i].size();++j) ^