04-00-functions.cpp

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

using namespace std;

double grade(double midterm, double final, double homework)
{
    return 0.2 * midterm + 0.4 * final + 0.4 * homework;
}

double median(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-1] + vec[mid]) / 2 :
        vec[mid];
}

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));
}

istream& read_hw(istream& in, vector<double>& hw)
{
    if(in) {
        // reset vector
        hw.clear();
        double x;
        while( in >> x )
            hw.push_back(x);
        // clear failure flag for istream
        in.clear();
    }
    return in;
}

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

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

    cout << "Enter all your homework grades, "
        "followed by end-of-file: ";

    vector<double> homework;

    read_hw(cin, homework);

    try {
        double final_grade = grade(midterm, final, homework);
        streamsize prec = cout.precision();
        cout << "Your final grade is " << setprecision(3)
            << final_grade << setprecision(prec) << endl;
    } catch (domain_error) {
        cout << endl << "You must enter your grades. "
            "Please try again" << endl;
        return 1;
    }
    return 0;
}