Compilare: user.cpp: In function ‘int query(Trie*, char*)’: user.cpp:41:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*w==NULL) ^ user.cpp: In function ‘int prefix(Trie*, char*, int)’: user.cpp:48:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*w==NULL || arbtr->fiu[*w-'a']==0) ^ user.cpp: In function ‘int main()’: user.cpp:55:33: 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:56:35: 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); ^ user.cpp:58:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%s",s); ^