商品折扣问题

#include <iostream>
using namespace std;
class Product
{
public:
	Product(int m,int q,float p):num(m),quantity(q),price(p){};
	void total();
	static float average();
	static void display();
private:
	int num;
	int quantity;
	float price;
	static float discount;
	static float sum;//销售总额
	static int n;//销售件数
};

void Product::total()//计算销售总额，统计件数
{
	float rate=1.0;
	if(quantity>10)
		rate=0.98*rate;
	sum=sum+quantity*price*rate*(1-discount);
	n=n+quantity;
}

void Product::display()
{
	cout<<"销售总额为 "<<sum<<",每件的平均售价为 ";
	cout<<average()<<endl;
}

float Product::average()//静态成员函数只能调用静态数据成员
{
	return(sum/n);
}
float Product::sum=0;
int Product::n=0;
float Product::discount=0.05;

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