Compilare: user.cpp: In member function ‘void Trie::add(char*)’: user.cpp:30:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^~~~ user.cpp: In member function ‘void Trie::remove(char*)’: user.cpp:49:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^~~~ user.cpp: In member function ‘int Trie::count(char*)’: user.cpp:68:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^~~~ user.cpp: In member function ‘int Trie::prefixMax(char*)’: user.cpp:78:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^~~~ user.cpp: In function ‘int main()’: user.cpp:95:33: warning: format ‘%s’ expects argument of type ‘char*’, but argument 3 has type ‘char (*)[21]’ [-Wformat=] while(scanf("%d %s", &op, &s) == 2) ^ user.cpp:90:35: 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:91:37: 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); ^