Significance of Copy Constructor

// Program to demonstrate cases when copy constructor is called
#include <iostream>
class Circle
{
	private :
		int radius ;
		float x, y ;
	public :
		Circle( )
		{
			radius = x = y = 0 ;
		}
		Circle ( int rr, float xx, float yy )
		{
			radius = rr ;
			x = xx ;
			y = yy ;
		}
		Circle ( const Circle& c )
		{
			std::cout << "Copy constructor invoked" << std::endl ;
			radius = c.radius ;
			x = c.x ;
			y = c.y ;
		}	
		void showData( )
		{
			std::cout << "Radius = " << radius << std::endl ;
			std::cout << "X-Coordinate = " << x << std::endl  ;
			std::cout << "Y-Coordinate = " << y << std::endl ;
		}
		void setData ( Circle c )
		{
			radius = c.radius ;
			x = c.x ;
			y = c.y ;
		}
} ;
Circle fun( ) 
{
	Circle c ;
	return c ;
}
int main( )
{
	Circle c1 ( 10, 2.5, 3.5 ) ;
	
	Circle c2 = c1 ;
	c2.showData( ) ;
	
	Circle c3 ;
	c3.setData ( c1 ) ;
	c3.showData( ) ;
		
	Circle c4 = fun( ) ;
	c4.showData( ) ;
		
	return 0 ;
}