Compilare: user.cpp: In member function ‘void Trie::add_word(std::string)’: user.cpp:29:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.length(); i++) { ^ user.cpp: In member function ‘void Trie::rem_word(std::string)’: user.cpp:42:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.length(); i++) { ^ user.cpp: In member function ‘int Trie::num_of_occurances(std::string)’: user.cpp:55:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.length(); i++) { ^ user.cpp: In member function ‘int Trie::longest_common_prefix(std::string)’: user.cpp:67:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.length(); i++) { ^ user.cpp: In function ‘int main()’: user.cpp:86:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("trie.in","r",stdin); ^ user.cpp:87:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("trie.out","w",stdout); ^