main函数的实现为啥一定得用指针呢，为啥每一个函数都要写成虚函数，有别的实现代码吗？

Question

/*定义一个车(vehicle)基类，具有MaxSpeed、Weight等成员变量，Run、Stop等成员函数，由此派生出自行车(bicycle)类、汽车(motorcar)类。
自行车(bicycle)类有高度(Height)等属性，汽车(motorcar)类有座位数(SeatNum)等属性。从bicycle和motorcar派生出摩托车(motorcycle)类。
请分别将vehicle设置为虚基类和不设置vehicle为虚基类进行实验*/
#include <iostream>
#include<cstring>
using namespace std;
class vehicle
{
protected:
    int MaxSpeed;
    int Weight;
public:
    vehicle(int m1,int w1)
    {
        MaxSpeed=m1;
        Weight=w1;
    }
    vehicle(){};
    virtual void run()
    {
        cout<<"vehicle runs."<<endl;
    }
    virtual void show()
    {
        cout<<"vehicle MaxSpeed="<<MaxSpeed<<endl;
        cout<<"vehicle Weight="<<Weight<<endl;

    }
    virtual void stop()
    {
        cout<<"vehicle stop."<<endl;
    }
};
class bicycle:virtual public vehicle
{
protected:
    int heigh;
public:
    bicycle(int m2,int w2,int h1)
    {
       MaxSpeed=m2;
       Weight=w2;
       heigh=h1;
    }
    bicycle(){}
    virtual void run()
    {
        cout<<"bicycle runs."<<endl;
    }
    virtual void show()
    {
        cout<<"bicycle MaxSpeed="<<MaxSpeed<<endl;
        cout<<"bicycle Weight="<<Weight<<endl;
        cout<<"bicycle height="<<heigh<<endl;
    }
    virtual void stop()
    {
        cout<<"bicycle stops."<<endl;
    }
};
class motorcar:virtual public vehicle
{
protected:
    int SetNum;
public:
    motorcar(int m3,int w3,int s1)
    {
       MaxSpeed=m3;
       Weight=w3;
       SetNum=s1;
    }
    motorcar(){};
    virtual void run()
    {
        cout<<"motorcar runs."<<endl;
    }
    virtual void show()
    {
        cout<<"motorcar MaxSpeed="<<MaxSpeed<<endl;
        cout<<"motorcar Weight="<<Weight<<endl;
        cout<<"motorcar SetNum="<<SetNum<<endl;
    }
    virtual void stop()
    {
        cout<<"motorcar stops."<<endl;
    }
};
class motorcycle:public bicycle,public motorcar
{
public:
    motorcycle(int m4,int w4,int h2,int s2)
    {
        MaxSpeed=m4;
        Weight=w4;
        heigh=h2;
        SetNum=s2;
    }
    motorcycle(){};
    virtual void run()
    {
        cout<<"motorcycle runs."<<endl;
    }
    virtual void show()
    {
        cout<<"motorcycle MaxSpeed="<<MaxSpeed<<endl;
        cout<<"motorcycle Weight="<<Weight<<endl;
        cout<<"motorcycle heigh="<<heigh<<endl;
        cout<<"motorcycle SetNum="<<SetNum<<endl;
    }
    virtual void stop()
    {
        cout<<"motorcycle stops."<<endl;
    }
};


int main()
{
   vehicle v(108,20);
   bicycle b(103,30,40);
   motorcar m(180,43,53);
   motorcycle n(145,63,45,56);
   vehicle *a[4]={&v,&b,&m,&n};
   for(int i=0;i<4;i++)
   {
       a[i]->run();
       a[i]->show();
       a[i]->stop();
   }
}

Answer 1

这是面向对象的重要特征之一——多态，在大型应用程序中应用很广，你想象一个游戏，有很多角色，它们不同类型，如果想更新所有的角色，怎么办？可以将所有的类型都派生自同一个类，提供一个Update虚函数，所有类都要重写这个函数，然后用基类指针数组存储所有的子类对象，更新所有角色的话，直接遍历数组，调用Update，根据多态定义，调用的是子类的Update，这样就实现了对所有角色的更新。你可以看看我的专栏C++游戏编程系列，里面的程序框架就用了多态原理。