C++ Constructor Copy Constructor X(X&)

#include <iostream>
using namespace std;
class alpha//from  w ww .ja va 2 s.  c o m
{
   private:
       int data;
   public:
   alpha()                    //no-arg constructor
   { }
   alpha(int d)               //one-arg constructor
   { data = d; }
   alpha(alpha& a)            //copy constructor
   {
      data = a.data;
      cout << "\nCopy constructor invoked";
   }
   void display()             //display
   { cout << data; }
   void operator = (alpha& a) //overloaded = operator
   {
      data = a.data;
      cout << "\nAssignment operator invoked";
   }
};
int main()
{
   alpha a1(37);
   alpha a2;
   a2 = a1;                        //invoke overloaded =
   cout << "\na2="; a2.display();
   alpha a3(a1);                   //invoke copy constructor
   // alpha a3 = a1;                  //equivalent definition of a3
   cout << "\na3="; a3.display();
   cout << endl;
   return 0;
}