Compilare: user.cpp: In function ‘void Add(Trie*&, char*)’: user.cpp:18:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) ^ user.cpp: In function ‘int Cnt(Trie*&, char*)’: user.cpp:33:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) ^ user.cpp: In function ‘bool Delete(Trie*&, char*)’: user.cpp:45:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^ user.cpp: In function ‘int main()’: user.cpp:70:33: 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:71:35: 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); ^ /tmp/cc4B4QPh.o: In function `main': user.cpp:(.text.startup+0x58): warning: the `gets' function is dangerous and should not be used.