1.定義Date類 :

Date類中定義了三個私有資料成員(year ,month,day)

2.定義Student類:

在Student類中定義了兩個私有資料成員(name[] ,birthday)

3.將Student類 定義為Date類的友元類

4.Student類中的成員函式 都可以使用 Date類中的私有成員

#include<iostream>
using namespace std;
#include<string.h>
class Student;

class Date
{ friend class Student;
private: int year,month,day;
public:
	Date(int y=1992,int m=7,int d=1){ year=y;month=m;day=d;} 
};

class Student
 

{ private: 
   char name[10];
    Date birthday;
public:
	 Student(char *s,int y,int m,int d)
	 {   strcpy(name,s); 	 
	     birthday.year=y; birthday.month=m;birthday.day=d; }
  
  void show(){ cout<<name<<endl;
        cout<<birthday.year<<"/"<<birthday.month<<"/"<<birthday.day<<endl;
  }  
};

int main()
{ Student stu1("王闖",1992,7,8);
stu1.show();
}