Compilare: user.cpp: In function ‘int main()’: user.cpp:12:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("prefix.in", "r", stdin); ^ user.cpp:13:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ("prefix.out", "w", stdout); ^ user.cpp:16:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d\n", &t); ^ user.cpp:20:23: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets (str + 1); ^ /tmp/cc1z7T2b.o: In function `main': user.cpp:(.text.startup+0x76): warning: the `gets' function is dangerous and should not be used.