Compilare: user.cpp: In function ‘void Ins(Trie*, char*)’: user.cpp:20:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) Node->cnt++; ^ user.cpp: In function ‘int Del(Trie*, char*)’: user.cpp:30:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) Node->cnt--; ^ user.cpp: In function ‘void Ap(Trie*, char*)’: user.cpp:45:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) printf("%d\n",Node->cnt); ^ user.cpp: In function ‘void Pref(Trie*, char*)’: user.cpp:52:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL or Node->v[ch]==0){ ^ user.cpp: In function ‘int main()’: user.cpp:63:33: 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:64:35: 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/cc38RM4d.o: In function `main': user.cpp:(.text.startup+0x6a): warning: the `gets' function is dangerous and should not be used.