多层派生时的构造函数

#include <iostream>
#include <string.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std;

class Student
{
    public:
        Student(int n,string nam)
        {
            num=n;
            name=nam;
        }
        void display()
        {
            cout<<"num:"<<num<<endl;
            cout<<"name:"<<name<<endl;
        }
        
        protected:
            int num;
            string name;
};

class Student1:public Student
{
    public:
        Student1(int n,string nam,int a):Student(n,nam)
        {
        age=a;
        }
        void show()
        {
            display();
            cout<<"age:"<<age<<endl;
        }
        private:
            int age;
};

class Student2:public Student1
{
    public:
        Student2(int n,string nam,int a ,int s):Student1(n,nam,a)
        {
            score=s;
        }
        void show_all()
        {
            show();
            cout<<"score:"<<score<<endl;
        }
        private:
            int score;
};

int main(int argc, char** argv) {
    Student2 stud(10010,"li",17,89);
    stud.show_all();
    return 0;
}