Compilare: user.cpp: In function ‘void intr(trie*, char*)’: user.cpp:24:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) ^ user.cpp: In function ‘int del(trie*, char*)’: user.cpp:39:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) ^ user.cpp: In function ‘int nr_ap(trie*, char*)’: user.cpp:58:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL) ^ user.cpp: In function ‘int pre(trie*, char*, int)’: user.cpp:67:12: warning: NULL used in arithmetic [-Wpointer-arith] if(*s==NULL||!nod->fiu[*s-'a']) ^ user.cpp:70:1: warning: control reaches end of non-void function [-Wreturn-type] } ^