C#复习，输入学生信息排列成绩

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

namespace ConsoleApplication4
{
    class Program
    {
        struct swe
        {
            public int xuhao;
            public string xuehao;
            public string xingming;
            public double chengji;
        }
        static void Main(string[] args)
        {
            ArrayList al = new ArrayList();
            Console.WriteLine("请输入班级人数：");
            int n = int.Parse(Console.ReadLine());
            for (int i = 1; i <= n; i++)
            {
                swe s = new swe();
                s.xuhao = i;
                while (true)
                {
                    Console.WriteLine("请输入第{0}个学生的学号：", i);
                    s.xuehao = Console.ReadLine();
                    if (s.xuehao == "")
                    {
                        Console.WriteLine("学号不能为空！");
                    }
                    else
                    {
                        break;
                    }
                }
                while (true)
                {
                    Console.WriteLine("请输入第{0}个学生的姓名：", i);
                    s.xingming = Console.ReadLine();
                    if (s.xingming == "")
                    {
                        Console.WriteLine("姓名不能为空！");
                    }
                    else
                    {
                        break;
                    }
                }
                while (true)
                {
                    Console.WriteLine("请输入第{0}个学生的成绩;", i);
                    try
                    {
                        s.chengji = int.Parse(Console.ReadLine());
                        if (s.chengji >= 0 && s.chengji <= 100)
                        {
                            break;
                        }
                        else
                        {
                            Console.WriteLine("成绩必须在0~100之间！");
                        }
                    }
                    catch
                    {
                        Console.WriteLine("成绩输入有误！");
                    }
                }
                al.Add(s);
                Console.WriteLine();
                for (int e = 0; e < al.Count - 1; e++)
                {
                    for (int j = e + 1; j < al.Count; j++)
                    {
                        swe s1 = (swe)al[e];
                        swe s2 = (swe)al[j];
                        if (s1.chengji < s2.chengji)
                        {
                            swe zhong = (swe)al[e];
                            al[e] = al[j];
                            al[j] = zhong;
                        }
                    }
                }
            }
            Console.WriteLine("序号 学号 姓名 成绩 ");
            foreach (object qq in al)
            {
                Console.WriteLine(((swe)qq).xuhao + "      " +
                ((swe)qq).xuehao + "    " +
                ((swe)qq).xingming + "    " +
                ((swe)qq).chengji);
            }