/in/foo.cc: In function 'int main()':
/in/foo.cc:38:2: error: 'cin' was not declared in this scope
  cin>>n>>k;
  ^~~
/in/foo.cc:52:3: error: 'cout' was not declared in this scope
   cout<<setw(ans2)<<grade[i].xuehao<<"  ";
   ^~~~
/in/foo.cc:56:36: error: 'endl' was not declared in this scope
   cout<<setw(ans3)<<grade[i].x[0]<<endl;
                                    ^~~~