// 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;
}

