Containership : Classes within classes

As we know that , inheritance is the mechanism of the deriving certain or all properties of one class (base class) into another class (derived class).

Cpp also supports another way of inheriting properties of one class into another class. This approach takes a view that an object is a collection of many other objects. That is a class can contain object objects of another classes as its  members.

A class which contains the object of another class is called container class and this kind of relationship is called containership.

#include<iostream.h>
#include<conio.h>
class date
{
int dd,mm,yyyy;
public:
date( )
{
dd=0 ; mm=0 ; yyyy=0;
}
void read_date(void)
{
cout<<"(dd mm yyyy) :";
cin>>dd>>mm>>yyyy;
}
void display_date(void)
{
cout<<dd<<"\\"<<mm<<"\\"<<yyyy;
}
};
class student
{
int roll_no;
char name[20];
date dob;    //Creating object of data class
public:
void read_student(void)
{
cout<<"\nEnter roll number :";
cin>>roll_no;
cout<<"Enter name :";
cin>>name;
cout<<"Enter date of birth";
dob.read_date( );       // Calling date class function
}
void display(void)
{
cout<<"\nRoll Number :"<<roll_no;
cout<<"\nName :"<<name;
cout<<"\nDate of birth :";
dob.display_date( );
}
};
main( )
{
clrscr( );
student s;
s.read_student( );
s.display( );
getch( );
return(0);
}

Output:-
Enter roll number :101
Enter name : Irawen
Enter date of birth (dd mm yyyy) : 27 10 81
Roll Number : 101
Name : Irawen
Date of birth : 27\10\81