Class ReferenceDemo
{
  public void swap(ref int a,ref int b)
  {
    int c;
    c=a;
    a=b;
    b=c;
    MessageBox.Show("A="+a.toString() + "B=" + b.toString());
  }
}
private void button1_click(Object sender,EventArgs e)
{
  ReferenceDemo obj=new ReferenceDemo();
  int x,y;
  x=10;
  y=20;
  obj.swap(ref x,ref y);
  MessageBox.Show("X=" + x.toString() + "Y=" + y.toString());
}