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:47:31: 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, int)’: user.cpp:89:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz != s.size()) index = s[poz] - 'a'; ^ user.cpp:97:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (poz == s.size()) ^ user.cpp: In function ‘int main()’: user.cpp:131:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < s.size(); j++) ^ user.cpp:156:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < s.size(); j++) ^ user.cpp:170:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < s.size(); j++) ^