C++语言基础 例程 多态性的概念

贺老师的教学链接  本课讲解

一种死板的机制

#include <iostream>#include <string>
using namespace std;
//声明基类Student
class Student
{
public:
    Student(int, string,float);//声明构造函数
    void display( );                                             //声明输出函数
protected:                                      //受保护成员，派生类可以访问
    int num;
    string name;
    float score;
};
//Student类成员函数的实现
Student::Student(int n, string nam,float s)
{
    num=n;    //定义构造函数
    name=nam;
    score=s;
}


void Student::display( )                                        //定义输出函数
{
    cout<<"num:"<<num<<"\nname:"<<name<<"\nscore:"<<score<<"\n\n";
}
//声明公用派生类Graduate
class Graduate:public Student
{
public:
    Graduate(int, string, float, float);                          //声明构造函数
    void display( );                                             //声明输出函数
private:
    float pay;
};
// Graduate类成员函数的实现
void Graduate::display( )                                       //定义输出函数
{
    cout<<"num:"<<num<<"\nname:"<<name<<"\nscore:"<<score<<"\npay="<<pay<<endl;
}


Graduate::Graduate(int n, string nam,float s,float p):Student(n,nam,s),pay(p) { }


//主函数
int main()
{
    Student stud1(1001,"Li",87.5);                   //定义Student类对象stud1
    Graduate grad1(2001,"Wang",98.5,563.5);          //定义Graduate类对象grad1
    Student *pt=&stud1;                              //定义指向基类对象的指针变量pt
    pt->display( );
    pt=&grad1;
    pt->display( );
    return 0;
}

运行中的动态是这样的！

#include <iostream>#include <string>using namespace std;//声明基类Studentclass Student{public:    Student(int, string,float);//声明构造函数    virtual void display( );                                             //声明输出函数protected:                                      //受保护成员，派生类可以访问    int num;    string name;    float score;};//Student类成员函数的实现Student::Student(int n, string nam,float s){    num=n;    //定义构造函数    name=nam;    score=s;}void Student::display( )                                        //定义输出函数{    cout<<"num:"<<num<<"\nname:"<<name<<"\nscore:"<<score<<"\n\n";}//声明公用派生类Graduateclass Graduate:public Student{public:    Graduate(int, string, float, float);                          //声明构造函数    void display( );                                             //声明输出函数private:    float pay;};// Graduate类成员函数的实现void Graduate::display( )                                       //定义输出函数{    cout<<"num:"<<num<<"\nname:"<<name<<"\nscore:"<<score<<"\npay="<<pay<<endl;}Graduate::Graduate(int n, string nam,float s,float p):Student(n,nam,s),pay(p) { }//主函数int main(){    Student stud1(1001,"Li",87.5);                   //定义Student类对象stud1    Graduate grad1(2001,"Wang",98.5,563.5);          //定义Graduate类对象grad1    Student *pt=&stud1;                              //定义指向基类对象的指针变量pt    pt->display( );    pt=&grad1;    pt->display( );    return 0;}