What is Copy Constructors?

A copy constructor is used to declare and initialize an object from another object.
class integer
{
         private : int m;
         public: integer( integer & x) //copy constructor
         { 

                  m = x.m; 

          }
};
integer a;
integer b(a); //copy constructor called
integer c=a; //copy constructor called again

Let us an example:

#include<iostream.h>
class cse
{
         int count;
         public:cse(){ }
         cse(int a)
         { 
               count=a; 
          }
          cse(cse &);
          void display()
          { 
                   cout<<count<<"\n"; 
          }
};
cse :: cse(cse &x)
{
         count=x.count;
}
void main()
{
       cse x1(100);
       cse x2(x1);
       cse x3=x1;
       x1.display();
       x2.display();
       x3.display();
}

Sample Output: