foo.c: In function 'main':
foo.c:15:10: error: array size missing in 'a'
   15 |  int n,i,a[];
      |          ^
foo.c:18:14: error: expected ';' before 'printf'
   18 |   n=f(n,a[i])
      |              ^
      |              ;
   19 |  printf("%d",n);
      |  ~~~~~~       

[Hydro](https://hydro.ac)提供评测服务