public class Student : IComparable
{
    public double mygrade;
    public string mysubject, myID;
    public Student() { }
    public Student(double grade, string subject, string id)
    {
        mygrade = grade;
        mysubject = subject;
        myID = id;
    }
    int IComparable.CompareTo(Object obj)
    {
        if(obj is Student)
        {
            Student s = (Student)obj;
            if(this.mygrade > s.mygrade)
            {
                return 1;
            }
            else if(this.mygrade < s.mygrade)
            {
                return -1;
            }
            else
            {
                return 0;
            }
        }
        throw new ArgumentException("object is not a Student");
    }
}

internal class Program
{

    private static void Main(string[] args)
    {
        Student[] students = new Student[5];
        students[0] = new Student(50.0, "windows程序设计", "001");
        students[1] = new Student(90.0, "windows程序设计", "002");
        students[2] = new Student(100.0, "windows程序设计", "003");
        students[3] = new Student(70.0, "windows程序设计", "004");
        students[4] = new Student(80.0, "windows程序设计", "005");
        Array.Sort(students);
        foreach(Student student in students)
        {
            Console.WriteLine(student.mygrade + "," + student.mysubject + "," + student.myID);
        }
    }

}