foo.cc: In function 'int main()':
foo.cc:17:10: error: 'floor' was not declared in this scope
  cout << floor (l / r) << endl;
          ^~~~~
foo.cc:17:10: note: suggested alternative: 'float'
  cout << floor (l / r) << endl;
          ^~~~~
          float

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