c#记事本搜索字符串操作

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace 甲骨文文字处理1._0
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox2.Text = "";
            label2.Text = "";
            int i=0,m=0;
            int num = 0;
            string[] filelist = File.ReadAllLines("1.txt", Encoding.Default);
            for (int linenum = 0; linenum <= filelist.Length - 1; linenum++) 
            {

                if (filelist[linenum].IndexOf("id=" + textBox1.Text) > -1)
                {
                    i++;
                    if (i == 1)
                    {
                        for (int lin = num + 2; lin <= linenum; lin++)
                        {
                            textBox2.AppendText(filelist[lin] + "\n");
                        }
                    }
                }
                if (filelist[linenum].IndexOf("id") > -1) 
                {
                    m++;
                    num = linenum;
                }

            }
            
            string sj = Convert.ToString(m);
            label2.Text = "1.txt文件中甲骨文信息已经添加了" + sj + "条记录！";
            
        }
    }
}