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

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

int main()
{
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	cout << "Please enter yourmidterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

	cout << "Enter all your homework grades, "
		"followed by endoffile:";
	vector<double> homework;
	double x;

	while (cin >> x)
		homework.push_back(x);
	typedef vector<double>::size_type vec_sz;  // 요기 에러1
	vec_sz size = homework.size();             // 요기 에러2
	if(size == 0) {
		cout << endl << "You must enter your grades. "
			"Please try again." << endl;

		return 1;
	}

	sort(homework.begin(),homework.end());
	vec_sz mid = size/2;                       // 요기 에러3
	double median;
	median = size %2 == 0 ? (homework[mid] + homework[mid-1])/2
		:homework[mid];

	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;
}