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)); }