#include<stdio.h> #include<iostream> using namespace std; class Goods { public: virtual double goodsprice()=0; virtual double show()=0; ~Goods(){} }; class rice: public Goods { private: double weight; double price; double goodsprice() { return weight*price; } public: rice(){} rice(const double w,const double p) { weight=w; price=p; } double show() { return goodsprice(); } friend double total(const rice r,const pork p,const oil o); }; class pork : public Goods { private: double weight; double price; double goodsprice() { return weight*price; } public: pork(const double w,const double p) { weight=w; price=p; } double show() { return goodsprice(); } friend double total(const rice r,const pork p,const oil o); }; class oil : public Goods { private: double weight; double price; double goodsprice() { return weight*price; } public: oil(const double w,const double p) { weight=w; price=p; } double show() { return goodsprice(); } friend double total(const rice r,const pork p,const oil o); }; double total(const rice r,const pork p,const oil o) { return (r.goodsprice()+p.goodsprice()+o.goodsprice()); } int main() { rice r(5.0,2.4); pork p(2.0,10.0); oil o(1.0,50.0); cout<<"大米价格为"<<r.show()<<"元"<<endl; cout<<"猪肉价格为"<<p.show()<<"元"<<endl; cout<<"油价格为"<<o.show()<<"元"<<endl; //cout<<"商品的总价格为"<<total()<<"元"<<endl; system("pause"); return 0; } 哪里错了

代码中存在以下几个问题：

1. 头文件 `<iostream>` 应该改为 `<iostream.h>`，因为这是 C++ 的标准头文件。

2. `show()` 和 `goodsprice()` 方法的返回值类型应该是 `double`，而不是 `void`。

3. `total()` 函数中的参数应该是对象的引用（即加上 `&` 符号），而不是对象本身。

4. `total()` 函数中的 `goodsprice()` 方法应该改为对象的公有方法，而不是私有方法。

下面是修改后的代码：

#include<stdio.h>
#include<iostream.h>

using namespace std;

class Goods {
public:
    virtual double goodsprice() = 0;
    virtual double show() = 0;
    virtual ~Goods(){}
};

class rice: public Goods {
private:
    double weight;
    double price;
    double goodsprice()
    {
        return weight * price;
    }
public:
    rice(){}
    rice(const double w, const double p)
    {
        weight = w;
        price = p;
    }
    double show()
    {
        return goodsprice();
    }
    friend double total(const rice& r, const pork& p, const oil& o);
};

class pork : public Goods {
private:
    double weight;
    double price;
    double goodsprice()
    {
        return weight * price;
    }
public:
    pork(const double w, const double p)
    {
        weight = w;
        price = p;
    }
    double show()
    {
        return goodsprice();
    }
    friend double total(const rice& r, const pork& p, const oil& o);
};

class oil : public Goods {
private:
    double weight;
    double price;
    double goodsprice()
    {
        return weight * price;
    }
public:
    oil(const double w, const double p)
    {
        weight = w;
        price = p;
    }
    double show()
    {
        return goodsprice();
    }
    friend double total(const rice& r, const pork& p, const oil& o);
};

double total(const rice& r, const pork& p, const oil& o) {
    return (r.show() + p.show() + o.show());
}

int main() {
    rice r(5.0, 2.4);
    pork p(2.0, 10.0);
    oil o(1.0, 50.0);
    cout << "大米价格为" << r.show() << "元" << endl;
    cout << "猪肉价格为" << p.show() << "元" << endl;
    cout << "油价格为" << o.show() << "元" << endl;
    cout << "商品的总价格为" << total(r, p, o) << "元" << endl;
    system("pause");
    return 0;
}