// reading from file

#include <fstream>	 // to read from files or write to files
#include <iostream>  // cin, cout
using namespace std;

int main()
{
	double pricePerBook = 0.0;	
	double bookShipping = 0.0;
	int numBooks = 0;
	double totalPrice = 0.0;

	ifstream infile("C:/Temp/a3data.txt");

	// or
	// ifstream infile;
	// infile.open("C:/Temp/a3data.txt");

	infile >> pricePerBook;
	infile >> bookShipping;

	infile.close();

	cout << "How many books? ";
	cin >> numBooks;

	double bookSubtotal = pricePerBook * numBooks + bookShipping * numBooks;
	cout << bookSubtotal << endl;

	ofstream outfile("C:/Temp/output.txt", ios::app); // append mode
	outfile << bookSubtotal << endl;

	outfile.close();

	return 0;
}