Compilare: user.cpp: In member function ‘void Trie::insert(std::string, int, int)’: user.cpp:39:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz != s.size()) index = s[poz] - 'a'; ^ user.cpp:41:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz != s.size() && this->fii[index] == NULL) ^ user.cpp:44:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz != s.size()) ^ user.cpp: In member function ‘std::string Trie::find(std::string, std::string, int)’: user.cpp:80:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz != s.size()) index = s[poz] - 'a'; ^ user.cpp:88:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz == s.size()) ^ user.cpp: In function ‘int main()’: user.cpp:121:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < names[i].size(); j++) ^ user.cpp:148:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < s.size(); j++) ^ user.cpp:165:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < s.size(); j++) ^