main1.cpp

这是Accelerated C++的配套源码

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

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

// compute the median of a `vector<double>'
// note that calling this function copies the entire argument `vector'
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] + vec[mid-1]) / 2 : vec[mid];
}

// compute a student's overall grade from midterm and final exam grades and homework grade
double grade(double midterm, double final, double homework)
{
	return 0.2 * midterm + 0.4 * final + 0.4 * homework;
}

// compute a student's overall grade from midterm and final exam grades
// and vector of homework grades.
// this function does not copy its argument, because `median' does so for us.
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));
}

// read homework grades from an input stream into a `vector<double>'
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 input will work for the next student
		in.clear();
	}
	return in;
}


int main()
{
	// ask for and read the student's name
	cout << "Please enter your first name: ";
	string name;
	cin >> name;
	cout << "Hello, " << name << "!" << endl;

	// ask for and read the midterm and final grades
	cout << "Please enter your midterm and final exam grades: ";
	double midterm, final;
	cin >> midterm >> final;

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

	vector<double> homework;

	// read the homework grades
	read_hw(cin, homework);

	// compute and generate the final grade, if possible
	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;
}