#include<iomanip>
#include<ios>
#include<iostream>
#include<string>

using std::cin;
using std::cout;
using std::endl;
using std::setprecision;
using std::string;
using std::streamsize;

int main()
{
  //请求输入并读入学生的姓名
  cout << "Please Enter your name:";
  string name;
  cin >> name;
  cout << "Hello," << name << "!" << endl;

  //请求输入并读入其中和期末成绩
  cout <<  "Please Enter your midterm and final exam grades:";
  double midterm,final;
  cin >> midterm >> final;

  //请求输入家庭作业成绩
  cout << "Enter all your homework grades," "Followed by end-of-file:";

  //到目前为止，读到的家庭作业成绩的个数及总和
  int count = 0;
  double sum = 0;

  //将家庭作业成绩读到变量x中
  double x;

  while (cin>>x) {
    ++count;
    sum += x;
  }
  streamsize prec = cout.precision();
  cout << "Your final grade is" << setprecision(3)
  << 0.2 * midterm + 0.4 *final + 0.4 *sum /count << setprecision(prec) << endl;
  return 0;
}

#include<algorithm>
#include<iomanip>
#include<ios>
#include<iostream>
#include<string>
#include<vector>

using namespace std;
int main()
{
  //请求输入并读入学生姓名
  cout << "Please Enter Your Name:";
  string name;
  cin >> name;
  cout << "Hello," << name << "!" << endl;

  //请求输入并读入其中和期末成绩
  cout << "Please Enter Your midterm and final exam grades:";
  double midterm,final;
  cin >> midterm >> final;

  //请求输入家庭作业成绩
  cout << "Enter all your homework grades," "Followed by end-of-file:";

  vector<double> homework;
  double x;

  //不变式：homework包含所有的家庭作业成绩
  while (cin>>x)
    homework.push_back(x);

 //检查homework是否为空
 typedef vector<double>::size_type vec_sz;
 vec_sz size = homework.size();
 if (size == 0) {
   cout << endl << "You must enter your grades." "Please tyr again." << endl;
   return 1;
 }

 //对成绩进行排序
 sort(homework.begin(),homework.end());

 //计算家庭作业成绩的中值
 vec_sz mid = size/2;
 double median;
 median = size % 2 == 0?(homework[mid]+homework[mid-1])/2:homework[mid];

 //计算并输出总成绩
 streamsize prec = cout.precision();
 cout << "Your final grade is" << setprecision(3)
 << 0.2 * midterm + 0.4 *final + 0.4 *median << setprecision(prec) << endl;
 return 0;
}