foo.cc: In function 'int main()':
foo.cc:6:2: error: 'cin' was not declared in this scope
  cin>>x>>y;
  ^~~
foo.cc:6:2: note: suggested alternative: 'main'
  cin>>x>>y;
  ^~~
  main
foo.cc:7:2: error: 'cout' was not declared in this scope
  cout<<x+y;
  ^~~~

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