Compilare: user.cpp: In function ‘int main()’: user.cpp:46:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cifra.in","r",stdin); ^ user.cpp:47:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cifra.out","w",stdout); ^ user.cpp:49:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d ",&n); ^ user.cpp:52:16: warning: ignoring return value of ‘char* gets(char*)’, declared with attribute warn_unused_result [-Wunused-result] gets(s); ^ user.cpp: In function ‘int calc(int, int)’: user.cpp:43:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ /tmp/ccINlvJV.o: In function `main': user.cpp:(.text.startup+0x80): warning: the `gets' function is dangerous and should not be used.