foo.c: In function 'FindNumbers':
foo.c:23:22: error: subscripted value is neither array nor pointer nor vector
   23 |                 if (a[i] < 0)
      |                      ^
foo.c:25:41: error: 'n' undeclared (first use in this function)
   25 |                 for (int j = i + 1; j < n; j++)
      |                                         ^
foo.c:25:41: note: each undeclared identifier is reported only once for each function it appears in
foo.c:27:30: error: subscripted value is neither array nor pointer nor vector
   27 |                         if (a[i] == a[j])
      |                              ^
foo.c:27:38: error: subscripted value is neither array nor pointer nor vector
   27 |                         if (a[i] == a[j])
      |                                      ^
foo.c:28:34: error: subscripted value is neither array nor pointer nor vector
   28 |                                 a[j] = -1;
      |                                  ^

[Hydro](https://hydro.ac)提供评测服务