Compilare: user.cpp: In function ‘void add(Trie*, char*)’: user.cpp:19: warning: NULL used in arithmetic user.cpp: In function ‘int del(Trie*, char*)’: user.cpp:31: warning: NULL used in arithmetic user.cpp: In function ‘int query(Trie*, char*)’: user.cpp:48: warning: NULL used in arithmetic user.cpp: In function ‘int prefix(Trie*, char*, int)’: user.cpp:56: warning: NULL used in arithmetic user.cpp: In function ‘int main()’: user.cpp:63: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:64: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:69: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result /tmp/cc4NC1d4.o: In function `main': user.cpp:(.text+0x2c1): warning: the `gets' function is dangerous and should not be used.