Compilare: user.cpp: In member function ‘void Trie::ins(Nod*, char*)’: user.cpp:35:16: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL){ ^ user.cpp: In member function ‘bool Trie::del(Nod*, char*)’: user.cpp:46:16: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL){ ^ user.cpp: In member function ‘int Trie::query(Nod*, char*)’: user.cpp:60:16: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL){ ^ user.cpp: In member function ‘int Trie::pre(Nod*, char*, int)’: user.cpp:69:16: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL||x->fii[Tr(s)]==nullptr){ ^ user.cpp: In function ‘char* ConvertStringToChar(std::__cxx11::string)’: user.cpp:84:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();i++){ ^ user.cpp:87:18: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] chr[s.size()]=NULL; ^