foo.cc: In function 'int main()':
foo.cc:7:6: warning: unused variable 'i' [-Wunused-variable]
  int i;
      ^
foo.cc:8:6: warning: unused variable 'cnt' [-Wunused-variable]
  int cnt=0;
      ^~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。