Compilare: user.cpp: In function ‘void add_trie(trie*, char*)’: user.cpp:27:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^ user.cpp: In function ‘void longest_prefix(trie*, char*)’: user.cpp:60:14: warning: NULL used in arithmetic [-Wpointer-arith] if(*s == NULL) ^ user.cpp: In function ‘int main()’: user.cpp:74:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sub.in", "r", stdin); ^ user.cpp:75:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sub.out", "w", stdout); ^ user.cpp:81:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &n); ^ user.cpp:85:18: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(str); ^ user.cpp:95:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n", &m); ^ user.cpp:99:18: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(str); ^ /tmp/cccK4NFZ.o: In function `main': user.cpp:(.text.startup+0x9d): warning: the `gets' function is dangerous and should not be used.