Which of the following statement is correct about the program given below?

#include<iostream.h> 
int x, y; 
class AptitudeTest
{
    public:
    AptitudeTest(int xx = 0, int yy = 0)
    {
        x = xx;
        y = yy;
        Display(); 
    } 
    void Display()
    {
        cout<< x << ' ' << y << ' ';
    }
};
int main()
{
    AptitudeTest objBT(10, 20); 
    int &rx = x; 
    int &ry = y; 
    ry = x;
    rx = y;
    cout<< rx--; 
    return 0; 
}