void Library::check_out(Patron p, Book b) { // Checks out a book in the library
	if (!find_book(b)) throw Library_error{};

	if (!find_patron(p)) throw Library_error{};

	if (p.check_fee()) { // Check if patron owes a fee
		char ch;
		cout << "This patron owes fee. Do you want to issue him the book(s)? (y or n)" << endl;
		cin >> ch;
		if (ch == 'n') return;
		if (ch != 'y') error("Wrong character detected\n");
	}