foo.c: In function 'main':
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", & n);
  ^~~~~~~~~~~~~~~~
foo.c:12:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", &a[i]);
   ^~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务