static void Main()
        {
            var names = new MyChildClass();

            names[DataColumns.Grades, 1]   = 'S';
            names[DataColumns.NameList, 9] = "W.S";
        }
        static void Main_01(string[] args)
        {
            Console.WriteLine("Hello World!");
            MyBaseClass b = new MyBaseClass(); //base

            Console.WriteLine(b.sum(3, 2));
            MyBaseClass bc = new MyChildClass();//Child

            Console.WriteLine(bc.sum(5, 2));
            MyChildClass c = new MyChildClass(); //child

            Console.WriteLine(c.sum(30, 2));
        }