Compilare: main.cpp: In function 'void add(std::__cxx11::string, int)': main.cpp:21:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (it < S.size() && node->v[S[it] - 'a'] != NULL){ ~~~^~~~~~~~~~ main.cpp:25:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (it < S.size()){ ~~~^~~~~~~~~~ main.cpp: In function 'void find_matches(std::__cxx11::string)': main.cpp:47:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (it = 0; it < s.size(); ++it){ ~~~^~~~~~~~~~ main.cpp:53:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (jt = 0; jt < node->index.size(); ++jt){ ~~~^~~~~~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:98:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (j = 0; j < failed->v[i]->index.size(); ++j){ ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~