use of copy constructors

//Demonstrate the use of copy constructors
#include<iostream.h>
#include<stdlib.h>
#include<conio.h>

class A
{
       int p,q;
  public:
         A()                             //1st constructors
         {
               p=0; q=0;
         }
         A(int m,int n)    //2nd constructors
         {
               p=m; q=n;
         }
         A(A&b)          //copy constructors
         {
               p=b.p;
               q=b.q;
         }
         void showdata()
         {  cout<<p<<ends<<q<<endl;
         }
};

int main()
{
     A f1;
     A f2(1,2);
     A f3(f2);
     f1.showdata();
     f2.showdata();
     f3.showdata();
 getch();
}