Class within Class or Containership or Composition or Has a / Kind of relationship

If two classes are related with one another there can be two types of relationship between them : a kind of relationship and a has a relationship. The kind of relationship is supported by inheritance and a has a relationship is supported by composition or containership.


In Inheritance if a class Y derived from class X, we can say that the new class Y is like that old class X or "Y is a kind of X". This is because the class Y has all the characteristic of X & in addition of its own.

In a has a relationship you simply create objects of your existing class inside the new class . For example,  if there is a class called carburettor we can create an object of this class in the new class as shown below:
class carburettor.
{
};
class car
{
 carburettor c;
} ;

Ex:

#include<iostream.h>
#include<string.h>
class carburettor
{
    private:
                char type;
                float cost;
                char mfr[30];
    public:
                void setdata(char t,float c,char*m)
                {
                    type=t;
                    cost=c;
                    strcpy(mfr,m);
                }
                void displaydata()
                {
                    cout<<endl<<type<<endl<<cost<<endl<<mfr;
                }
};
class car
{
    private: char model[25];
                char derivetype[20];
    public: void setdata(char *m,char *d)
              {
                    strcpy(model,m);
                    strcpy(derivetype,d);
              }
              void displaydata()
              {
                    cout<<endl<<model<<endl<<derivetype;
              }
              carburettor c;//embedded object
};
void main()
{
    car mycar;
    mycar.c.setdata('A',8500,"Micro");
    mycar.setdata("sports","4-wheel");

    mycar.c.displaydata();
   mycar.displaydata();
}