求助:C#基数排序

using System;
using System.Text;
using System.Collections;
using System.IO;
using System.Data;

namespace a
{
        
    public class ListNode
    {
        public string[]keys;
        public ListNode link;
        public static int Length;
        public ListNode()
        {
            link=null;
            Length=0;
        }

        public ListNode(string[]key,int len)
        {
            int i=0;
            Length=len;
            keys=new string[len];
            foreach(string c in key)
            {
                keys[i]=c;
                i++;
            }
            link=null;

        }

    }


    public class List
    {
        private ListNode Head;
        private ListNode Tail;
        private ListNode Current;
        private int index;

        public List()
        {
            Head=null;
            Tail=null;
            index=0;
        }

        /// <summary>
        /// 尾部添加数据
        /// </summary>

        public void Append(string [] key,int n )
        {
            ListNode NewNode=new ListNode(key,n );
            if (index==0)  //如果头指针为空
            {
                Head=NewNode;
                Tail=NewNode;
            }
            else
            {
                Tail.link =NewNode;
                Tail=NewNode;
            }
            Current=NewNode;
            index+=1;//链表数据个数加一
        }
        
        public void print(int Len)
        {
            ListNode p=Head;
            int j=0;
            while(p!=null)
            {
                Console.Write("第{0}条记录  :",(j++).ToString());//Console.Write("第{}条记录:",j++);
                for(int i=0;i<Len;i++)
                    Console.Write("key[{0}]={1}  ",i.ToString(),p.keys[i]);
                Console.WriteLine();
                p=p.link;
            }
        }

        public void RadixSort(int d,int radix)   //基数排序
        {
            ListNode[]rear,front;
            rear=new ListNode[radix];
            front=new ListNode[radix];
            ListNode current=Head;

            for(int i=d-1;i>=0;i--)   
            {
                while(current!=null)    //将n个对象分配到radix个队列中去
                {
                    int k=Convert.ToInt32(current.keys[i]);  //取当前检测对象的第i个关键码
                    if(front[k].link==null)      //第k个队列空,该对象成为队头                        front[k]=current;   
                    else                    //不空,队尾结点链域指向它
                        rear[k].link=current;
                    rear[k]=current;        //该对象成为新的队尾
                    current=current.link ;
                }
                int j=0;        //依次从各个队列中把对象取出并拉链

                while(front[j].link==null) j++;   //找到第一个非空队列
                Head=current=front[j];
                ListNode last=rear[j];
                for(int k=j+1;k<radix;k++)     //连接其余的队列
                 if(front[k].link!=null)
                 {
                    last.link=front[k];
                    last=rear[k];
                 }
            }
        }
    }


    class sort
    {
        
        static void Main(string []args)
        {
            StreamReader sr = new StreamReader("d:\\abc.txt");
            string line = sr.ReadLine();
            string info = "";
            int len=0;
                
            if(line!=null)
            {
                string []s1=line.Split(new char[]{','});
                foreach(string c in s1)
                    len++;
            }
            else
            {
                Console.WriteLine("文件为空");
                return;
            }

            List p=new List();
            while(line != null)
            {
                info += line;
                line = sr.ReadLine();
                string[] s = info.Split(new char[]{','});
                p.Append(s,len);
                info="";
            }
            Console.WriteLine("初始化链表:");
            p.print(len);
            p.RadixSort(len,10);
            Console.WriteLine("排序后的链表:");
            p.print(len);
        }
    }

}

我这个程序是基数排序,从文件中读入数据,每条记录有n个关键字.
红色部分应该有问题,麻烦各位看看

调试时错误: if(front[k].link==null)      //第k个队列空,该对象成为队头

错误代码: 输入字符串的格式不正确。
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补充：.NET技术 ,  C#