关于C#的公车线路调用的程序，求各位大神帮忙

我假定了10条线路，button1的作用是起点到终点坐一条线直达，button2的作用是需换车的，但是button2有错误，运行不出来。（textBox1是起点，textBox2是终点）using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace bus_station
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        string[] bus = new string[10];        private void button1_Click(object sender, EventArgs e)
        {
            string path = " ";
            string aa = " ";
            for (int i = 0; i < bus.Length; i++)
            {
                aa = bus[i];
                if ((aa.IndexOf(textBox1.Text) >= 0) && (aa.IndexOf(textBox2.Text) >= 0))
                {
                    string[] b = aa.Split(',');
                    path += b[0];
                }
            }
            if (path != " ") textBox3.Text = path;
            else textBox3.Text = "没有合适的线路";        }
      
            private  string tr(string a, string b)
            {
                string ret = " ";
                string[] a1 = a.Split(',');
                string[] b1 = b.Split(',');
                for (int i = 0; i < a1.Length; i++)
                {
                    for (int j = 0; j < b1.Length; j++)
                    {
                        if (a1[i] == b1[j])
                        {
                            if (ret == "  ") ret = a1[i];                            else ret += "," + a1[i];
                        }
                    }
                }
                return ret;   
            }
             private void button2_Click(object sender, EventArgs e)
        {
            
            
            string path = " ";
            string aa = " ", bb = " ",cc=" ";
            for (int i = 0; i <bus.Length; i++)
            {
                aa = bus[i];
                if (aa.IndexOf(textBox1.Text) >= 0)
                {
                    for (int j = 0; j < bus.Length; j++)
                        if (i != j)
                        {
                            bb = bus[j];
                            if (bb.IndexOf(textBox2.Text) >= 0)
                            {
                                cc = tr(aa, bb);
                                if (cc != " ")
                                path += aa.Substring(0, 4) + "→" + cc+"转" + bb.Substring(0, 4) + "→" + textBox2.Text;
                            }
                        }
                }
            }
            if (path != " ") textBox3.Text = path;
            else textBox3.Text = "没有合适的线路";       }        private void Form1_Load(object sender, EventArgs e)
        {
            bus[0] = "#1,10,11,12,13,14,15,16,17,18,19";
            bus[1] = "#2,20,21,22,23,24,25,26,27,28,29";
            bus[2] = "#3,30,31,32,33,34,35,36,37,38,39";
            bus[3] = "#4,40,41,42,43,44,45,46,47,48,49";
            bus[4] = "#5,50,51,52,53,54,55,56,57,58,59";
            bus[5] = "#6,60,61,62,63,64,65,66,67,68,69";
            bus[6] = "#7,70,71,12,73,74,75,76,77,78,79";
            bus[7] = "#8,80,81,82,83,84,85,86,87,88,89";
            bus[8] = "#9,90,91,92,93,94,95,96,97,98,99";
            bus[9] = "#10,00,01,02,03,04,05,06,07,08,09";
        }                
    }
}