Compilare: user.cpp: In function ‘int main()’: user.cpp:12:41: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cal.in" , "r" , stdin ); ^ user.cpp:13:43: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("cal.out" , "w" , stdout ); ^ user.cpp:14:47: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d%d" , &x , &y , &S , &N ); ^ user.cpp:17:39: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d" , &x1 , &y1 ); ^