Compilare: user.cpp: In member function ‘void trie::ins(char*)’: user.cpp:25:18: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^ user.cpp: In member function ‘bool trie::del(char*)’: user.cpp:42:18: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^ user.cpp: In member function ‘int trie::que(char*)’: user.cpp:63:18: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^ user.cpp: In member function ‘int trie::pre(char*, int)’: user.cpp:75:18: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL || this->v[CH]==0) ^ user.cpp: In function ‘int main()’: user.cpp:96:27: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(fin,"%s",s); ^