/in/foo.cc: In function 'int main()':
/in/foo.cc:6:17: warning: unused variable 'mid' [-Wunused-variable]
  int n, a[101], mid, all, ans;
                 ^~~
/in/foo.cc:19:19: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%d", ans);
                   ^
/in/foo.cc:10:27: warning: 'all' may be used uninitialized in this function [-Wmaybe-uninitialized]
   scanf("%d", &a[i]), all += a[i];
                       ~~~~^~~~~~~