Thread: Visual C++ istream (Accelerated C++)

I am going through Accelerated C++ using Visual C++ express 2010. In chapter 4 it makes a struct for student info and supposedly reads names and marks in from a file, and this is where I am stumped. For those who don't have the book, the code is

Code:

#ifndef GUARD_Student_info
#define GUARD_Student_info

#include <iostream>
#include <string>
#include <vector>

struct Student_info {
	std::string name;
	double midterm, final;
	std::vector<double> homework;
};
bool compare(const Student_info&, const Student_info&);
std::istream& read(std::istream&, Student_info&);
std::istream& read_hw(std::istream&, std::vector<double>&);
#endif

Code:

#include "Student_info.h"

using std::istream;
using std::vector;

bool compare(const Student_info& x, const Student_info& y)
{
    return x.name < y.name;
}

istream& read(istream& is, Student_info& s)
{
    is >> s.name >> s.midterm >> s.final;

    read_hw(is,s.homework);     //read and store all the students' homework grades
    return is;
}

istream& read_hw(istream& in, vector<double>& hw)
{
    if(in)
    {
        //get rid of previous contents
        hw.clear();

        //read homework grades
        double x;
        while(in>>x)
         hw.push_back(x);

        //clear the stream so that the input would work for the next student
        in.clear();
    }

    return in;
}

Code:

#ifndef GUARD_grade_h
#define GUARD_grade_h

#include <vector>
#include "Student_info.h"

double grade(double, double, double);
double grade(double, double, const std::vector<double>&);
double grade(const Student_info&);

#endif

Code:

#include <stdexcept>
#include <vector>
#include "grade.h"
#include "median.h"
#include "Student_info.h"

using namespace std;

double grade(double midterm, double final, double homework)
{
	return 0.2 * midterm + 0.4*final+0.4*homework;
}
double grade(double midterm, double final, const vector<double>& hw)
{
	if (hw.size()==0)
		throw domain_error("student has done no homework");
	return grade(midterm, final, median(hw));
}
double grade(const Student_info& s)
{
	return grade(s.midterm, s.final, s.homework);
}

Code:

#ifndef GUARD_median_h
#define GUARD_median_h

#include <vector>
double median(std::vector<double>);

#endif

Code:

#include "median.h"
#include <vector>
#include <algorithm>

using std::istream;
using std::vector;
using std::sort;
using std::domain_error;

double median(std::vector<double> vec)
{
	typedef vector<double>::size_type vec_sz;

	vec_sz size = vec.size();
	if (size==0)
		throw domain_error("median of an empty vector");
	sort(vec.begin(), vec.end());

	vec_sz mid = size/2;
	return size % 2==0 ? (vec[mid] + vec[mid-1]) /2 : vec[mid];
}

and the main class

Code:

#include <iostream>
#include <iomanip>
#include <algorithm>
#include <ios>
#include <stdexcept>
#include <string>
#include <vector>
#include "grade.h"
#include "Student_info.h"

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

int main()
{
	vector<Student_info> students;
	Student_info record;
	string::size_type maxlen = 0;

	while (read(cin, record)) {
		maxlen = max(maxlen, record.name.size());
		students.push_back(record);
		cout << "entered";
		cout << students[0].name << string(maxlen+1 - students[0].name.size(), ' ');
	}
	sort(students.begin(), students.end(), compare);

	for(vector<Student_info>::size_type i=0;
		i != students.size(); ++i) {
			cout << students[i].name << string(maxlen+1 - students[i].name.size(), ' ');

			try {
				double final_grade = grade(students[i]);
				streamsize prec = cout.precision();
				cout << setprecision(3) << final_grade << setprecision(prec);
			} catch (domain_error e) {
				cout << e.what();
			}
			cout << endl;
	}
	cin.ignore();
	cin.get();
	return 0;
}

Initially I get a blank screen, I can input some values but no way of printing results out.