foo.cc: In function 'int main()':
foo.cc:9:23: warning: unused variable 'k' [-Wunused-variable]
    9 |         long n, i, j, k, tmp, x1, x2;
      |                       ^
foo.cc:9:26: warning: unused variable 'tmp' [-Wunused-variable]
    9 |         long n, i, j, k, tmp, x1, x2;
      |                          ^~~
foo.cc:9:31: warning: unused variable 'x1' [-Wunused-variable]
    9 |         long n, i, j, k, tmp, x1, x2;
      |                               ^~
foo.cc:9:35: warning: unused variable 'x2' [-Wunused-variable]
    9 |         long n, i, j, k, tmp, x1, x2;
      |                                   ^~

[Hydro](https://hydro.ac)提供评测服务