Compilare: user.cpp: In function ‘void initialize(trie*, char*)’: user.cpp:34:15: warning: NULL used in arithmetic [-Wpointer-arith] if (*s == NULL || lenght == 61) { ^ user.cpp: In function ‘void query(trie*, char*)’: user.cpp:58:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) { ^ user.cpp: In function ‘int main()’: user.cpp:88:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < strlen(substring[1]); i++) { ^ user.cpp:99:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < strlen(substring[i]); j++) { ^