static void Main()
{
Console.WriteLine(10 < 20);
Console.WriteLine(10.CompareTo(20)); // if 10 > 20 : -1, same : 0, 10 < 20 : 1
string s1 = "AA", s2 = "BB";
// Console.WriteLine(s1 < s2); error, relational operator only used for numeric associate type
Console.WriteLine(s1.CompareTo(s2)); // almost type, enable to compare
Point p1 = new Point(1, 1);
Point p2 = new Point(2, 2);
Console.WriteLine(p1.CompareTo2(p2));
// apply c# interface 2.0
cPoint p3 = new cPoint(1, 1);
cPoint p4 = new cPoint(2, 2);
Console.WriteLine(p3.CompareTo(p4));
object o2 = new cPoint(2, 2);
Console.WriteLine(p3.CompareTo(o2));
}