面向对象的程序设计：对象数组，对象指针书后习题——第九章（P295）第九题

原题见谭浩强C++课本第九章（P295）第九题

题目：商店销售某一商品，每天公布统一的折扣。同时允许销售人员在销售是灵活掌握售价，在此基础上，一次购时间以上者，享受98折优惠，现已知当天3个销售员销售情况为：

请编写程序，计算当日此产品的总销售款sum以及每件商品的平均单价，要求用静态成员和静态成员函数。

#include<iostream>
using namespace std;
class Sale {
private:
	int num;//工号
	int quantity;//每个人销售的件数
	double price;//销售单价
	static double sum;//总销售款
	static double discount;
	static int n;//总销售件数
public:
	Sale(int n, int q, double p) {
		num = n;
		quantity = q;
		price = p;
	}
	static double average();
	friend void inputdiscount();
	static void print(Sale s[]);
	void cal() {
		if (quantity <= 10) {
			sum += quantity * discount * price;
		}
		else {
			sum += quantity * discount * price * 0.98;
		}
		n += quantity;
	}

};
double Sale::sum = 0;
int Sale::n = 0;
double Sale::discount = 1;
void inputdiscount() {
	cin >> Sale::discount;
}




double Sale::average() {
	return sum / n;
}
void Sale::print(Sale s[]) {
	for (int i = 0; i < 3; i++) {
		cout << "number: " << s[i].num << " quantity: " << s[i].quantity << " price: " << s[i].price << endl;
	}
	cout << "sum: " << sum << " sum of quantity: " << n << " average: " << average() << endl;
}
int main() {
	Sale s[3]{
		Sale(101,5,23.5),
		Sale(102,12,23.56),
		Sale(103,100,21.5),
	};
	inputdiscount();
	for (int i = 0; i < 3; i++)
		s[i].cal();
	s[0].print(s);
}

输出结果：