指向基类对象的指针变量也可以指向派生类对象

#include <iostream>
#include <string>
using namespace std;
class Student//声明Student类
{
public:
    Student(int, string,float);
    void display( );
private:
    int num;
    string name;
    float score;
};

Student::Student(int n, string nam,float s)
{
    num=n;
    name=nam;
    score=s;
}

void Student::display( )
{
    cout<<endl<<"num:"<<num<<endl;
    cout<<"name:"<<name<<endl;
    cout<<"score:"<<score<<endl;
}

class Graduate:public Student
{
public:
    Graduate(int, string ,float,float);
    void display( );
private:
    float pay;
};

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

void Graduate::display()
{
    Student::display();
    cout<<"pay="<<pay<<endl;
}

int main()
{
    Student stud1(1001,"Li",87.5);
    Graduate grad1(2001,"Wang",98.5,563.5);
    Student *pt=&stud1;
    pt->display( );
    pt=&grad1;
    pt->display( );
    return 0;
}