Compilare: user.cpp: In function ‘void add(char*, Trie*)’: user.cpp:20:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*p == NULL){ ^ user.cpp: In function ‘int freq(char*, Trie*)’: user.cpp:33:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*p == NULL) ^ user.cpp: In function ‘int pref(char*, Trie*)’: user.cpp:42:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*p == NULL) ^ user.cpp: In function ‘bool _erase(char*, Trie*)’: user.cpp:51:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*p == NULL){ ^ user.cpp: In function ‘int freq(char*, Trie*)’: user.cpp:39:1: warning: control reaches end of non-void function [-Wreturn-type] } ^