求平均数，排列顺序为降序

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            ArrayList al = new ArrayList();

            Console.WriteLine("请输入人数");
            int n =int.Parse(Console.ReadLine());

            for (int i = 0; i < n; i++)
            {
                Console.Write("请输入第"+(i+1)+"个学生的分数：");

                al.Add(int.Parse(Console.ReadLine()));

           }
            double he = 0;
                for(int b =0;b<n;b++)

                {
                    he = he + double.Parse(al[b].ToString());
                }

            double pj = he  / n;

            Console.WriteLine("平均分为"+pj);

            al.Sort();
            al.Reverse();
            for (int d = 0; d < n; d++)
            {
                Console.WriteLine(al[d]);
            }

                Console.ReadLine();

        }
    }
}