#include <iostream>
using namespace std;
class product
{public:
    product(int n,int q,int p ):num(n),quantity(q),price(p){};
    int display();
private:
    int num;
    int quantity;
    int price;
    static int sum;
    static int n;
};   
int product:: display()
    {   
    int cout=0,i=0,n=0;
        
        for(i=0;i<3;i++)
        {
            cout<<"please input num,quantity and the price"<<endl;//错误'<<' : illegal, right operand has type 'char [40]'
            cin>>nu[i].num>>endl>>nu[i].quantity>>endl>>nu[i].price>>endl;//错误'nu' : undeclared identifier。
        if (quantity>10) price=0.98*price;
            sum+=price;
            n=n+quantity;}
        cout<<(sum/n);//警告<<' : operator has no effect; expected operator with side-effect
        return 0;
    }   
int product::sum=0;
int product::n=0;
int main()
{
    int x,y;
    product nu[3]={
    product (01,1,15),
    product (02,3,10),
    product (03,20,20)};
    int display();
   
    return 0;
}

求解

可先自己把提示语法错误解决。不懂的查词典或网络，进步比别人帮助的要大。