foo.cc: In function 'int main()':
foo.cc:5:6: warning: unused variable 'f' [-Wunused-variable]
    5 |  int f[100], a[100], i, j, k;
      |      ^
foo.cc:5:25: warning: unused variable 'j' [-Wunused-variable]
    5 |  int f[100], a[100], i, j, k;
      |                         ^
foo.cc:5:28: warning: unused variable 'k' [-Wunused-variable]
    5 |  int f[100], a[100], i, j, k;
      |                            ^

[Hydro](https://hydro.ac)提供评测服务