譚浩強c++第三版9-9

#include<iostream>
#include<iomanip>
using namespace std;

//商店銷售某一商品，每天公布統一的折扣

class Goods
{
public:
	Goods(int nu,int q,double p):num(nu),quantity(q),price(p){}
	void total();
	static double average();
	void display();
private:
	static double discount;
	static double sum;
	static int n;
	int num;
	int quantity;
	double price;
};

void Goods::total()
{
	double rate = 0.95;           //書上似乎沒有提到這個統一的折扣是95折。。。
	if (quantity > 10)
		sum += quantity * price * rate * discount;
	else sum += quantity * price * rate ;
	n += quantity;
}

double Goods::average()
{
	return sum / n;
}

void Goods::display()
{
	cout << "當日總貨款:" << sum << endl;
	cout << "當日平均售價:" << setiosflags(ios::fixed) << setprecision(2) << average() << endl;
}

double Goods::discount = 0.98;
double Goods::sum = 0;
int Goods::n = 0;

int main()
{
	Goods test[3] = {
		Goods(101,5,23.5),
		Goods(102,12,24.56),
		Goods(103,100,21.5)
	};
	for (int i = 0; i < 3; i++)
		test[i].total();
	test[2].display();
	return 0;
}