static void Main(string[] args)
        {
            PointS  ps  = new PointS(11);
            PointC  pc  = new PointC(11);
            PointS1 ps1 = new PointS1(17);

            TestStruct(ps1);
            TestClass(pc);
            WriteLine("PS1.X = " + ps1.Pc.X);
            WriteLine("PS.X = " + ps.X);

            WriteLine("PC.X = " + pc.X);
        }
 static void TestClass(PointC pc)
 {
     pc.X = 25;
 }