Question

我正在尝试实现使用继承/多态的类，我无法弄清楚为什么我将这个无效的操作数变为二进制表达式错误（＆＃34;基本的ostream char std 1 char traits char和void）。该错误位于下面称为animate的函数中，其中它被两个**包围，位于main的正上方。由于某种原因，c-＆gt;移动给出了这个错误，但是c-> name并不是。我已经实现了其他所有功能，其他一切似乎都能正常运行。这只是一个错误。有人可以解释一下发生了什么吗？基本上，这里的基类是生物，所有其他类都是从它派生的。

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


class Creature {
public:
    Creature(string new_name) {
        its_name=new_name;
    }
    virtual void move() const=0;
    virtual bool isMortal() const =0;
    string name() const {
        return its_name;
    }

    virtual ~Creature();

private:
    string its_name;

};

class Phoenix:public Creature {
public:
    Phoenix(string new_name):Creature(new_name) {};
    virtual void move() const{
        cout<<"Squawkes, who is immortal, will now fly.";
    }
    virtual bool isMortal() const {
        return false;
    }

    virtual ~Phoenix();
};

class Giant:public Creature {
public:  
    Giant(string new_name,int new_lbs): Creature(new_name) {
        lbs=new_lbs;

    }
    virtual void move() const {
        if (lbs<20) {
            cout<<"Frawp, who is mortal, will now tromp.";
        }
        else {
            cout<<"Gridwulfa, who is mortal, will now lumber.";
        }
    }
    virtual bool isMortal() const {
        return true;
    }

    virtual ~Giant();
private:
    int lbs;
};

class Centaur:public Creature {
public:
    Centaur(string new_name):Creature(new_name) {};
    virtual void move() const{
        cout<<"Squawkes, who is immortal, will now fly.";
    }
    virtual bool isMortal() const {
        return false;
    }

    virtual~Centaur();
};

void animate(const Creature* c)  //need to add & or is * sufficient?
{
    cout << c->name() << ", who is ";
    if (c->isMortal())
        cout << "mortal";
    else
        cout << "immortal";
    **cout << ", will now " << c->move() << ".\n";**
}

Here is my main:

int main() {

    Creature* creatures[4];
    creatures[0] = new Phoenix("Squawkes");
    // Giants have a name and a weight in tons.  Giants under 20 tons
    // walk by tromping; giants weighing at least 20 tons lumber.
    creatures[1] = new Giant("Frawp", 17);
    creatures[2] = new Giant("Gridwulfa", 22);
    creatures[3] = new Centaur("Florence");

    cout << "Here are the creatures." << endl;
    for (int k = 0; k < 4; k++)
        animate(creatures[k]);

    // Clean up the creatures before exiting
    cout << "Cleaning up." << endl;
    for (int k = 0; k < 4; k++)
        delete creatures[k];


}

我不应该改变主要或动画。我必须正确地实现所有类

Answer 1

您的函数的返回类型为void：

void Creature::move()

你不能向流发送空格，你需要返回一些可打印的东西，字符串，整数，布尔，等等......

Answer 2

试试这个......

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


class Creature {
public:
    Creature(string new_name) {
        its_name=new_name;
    }
    virtual std::string move() const=0;
    virtual bool isMortal() const =0;
    string name() const {
        return its_name;
    }

    virtual ~Creature();

private:
    string its_name;

};

class Phoenix:public Creature {
public:
    Phoenix(string new_name):Creature(new_name) {};
    virtual std::string move() const{
        return "fly";
    }
    virtual bool isMortal() const {
        return false;
    }

    virtual ~Phoenix();
};

class Giant:public Creature {
public:  
    Giant(string new_name,int new_lbs): Creature(new_name) {
        lbs=new_lbs;

    }
    virtual std::string move() const {
        if (lbs<20)
            return  "tromp";
        return "lumber";
    }
    virtual bool isMortal() const {
        return true;
    }

    virtual ~Giant();
private:
    int lbs;
};

class Centaur:public Creature {
public:
    Centaur(string new_name):Creature(new_name) {};
    virtual std::string move() const{
        return "fly";
    }
    virtual bool isMortal() const {
        return false;
    }

    virtual~Centaur();
};

void animate(const Creature* c)  //need to add & or is * sufficient?
{
    cout << c->name() << ", who is ";
    if (c->isMortal())
        cout << "mortal";
    else
        cout << "immortal";
    **cout << ", will now " << c->move() << ".\n";**
}


int main() {

    Creature* creatures[4];
    creatures[0] = new Phoenix("Squawkes");
    // Giants have a name and a weight in tons.  Giants under 20 tons
    // walk by tromping; giants weighing at least 20 tons lumber.
    creatures[1] = new Giant("Frawp", 17);
    creatures[2] = new Giant("Gridwulfa", 22);
    creatures[3] = new Centaur("Florence");

    cout << "Here are the creatures." << endl;
    for (int k = 0; k < 4; k++)
        animate(creatures[k]);

    // Clean up the creatures before exiting
    cout << "Cleaning up." << endl;
    for (int k = 0; k < 4; k++)
        delete creatures[k];


}

二进制表达式的操作数无效？

2 个答案: