Compilare: main.cpp: In function 'void erase_from_trie(Trie*&, std::__cxx11::string, int)': main.cpp:25:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (index == nw.size()) { ~~~~~~^~~~~~~~~~~~ main.cpp: In function 'int prefix(std::__cxx11::string, Trie*)': main.cpp:44:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = (0) ; i < nw.size() ; ++ i) { ~~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:52:41: 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) ; ^ main.cpp:53:43: 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) ; ^