/in/foo.cc: In function 'int main()':
/in/foo.cc:8:2: error: 'cout' was not declared in this scope
  cout << "请输入n的值：" << endl;
  ^~~~
/in/foo.cc:8:35: error: 'endl' was not declared in this scope
  cout << "请输入n的值：" << endl;
                                   ^~~~
/in/foo.cc:9:2: error: 'cin' was not declared in this scope
  cin >> n;
  ^~~