Compilare: user.cpp: In function ‘nod* add_str(nod*, const string&, int, std::vector<std::vector<nod*> >&)’: user.cpp:40:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < str.size(); ++i){ ^ user.cpp: In function ‘int main()’: user.cpp:122:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(nod *i = rad; str.size() < n; ){ ^