Compilare: user.c: In function ‘main’: user.c:30:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen(IN, "r", stdin); ^ user.c:31:12: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen(OUT, "w", stdout); ^ user.c:33:10: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf("%lu", &n); ^