اشکال در ویرایش فایل notpad در سی شارپ

[milititi*]

سلام...اطلاعات مشتری رو تو نوت پد ذخیره کردم-- کد رو میگیره..اگه همچین کدی بود مشخصات رو تو تکست باکسای مربوطه نشون میده
ولی بخوام اون رکرد نشون داده شده رو ویرایش کردم ذخیره بشه .... و یا پاک بشه ( البته با 2 دکمه جدا) انجام نمیشه ...بر نامم کجا ایراد داره!!!!!؟؟؟؟

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;namespace WindowsFormsApplication1
{
    public partial class customerinfo1 : Form
    {
        public class customers
        {
            public int idcustom,phone;
            public string family,company,address;
        }
        public customerinfo1()
        {
            InitializeComponent();
        }
        private void customer_Load(object sender, EventArgs e)
        {
            textBox4.Text = "";
        }

  //save customer    ذخيره اطلاعات مشتري
              private void button1_Click(object sender, EventArgs e)
        {
            customers cust = new customers();
            cust.idcustom = Int32.Parse(textBox1.Text);
            cust.family = textBox2.Text;
            cust.company = textBox3.Text;
            cust.phone = Int32.Parse(textBox4.Text);
            cust.address = textBox5.Text;
            if (!File.Exists("c: \\ porozhe.txt"))
            {
                using (StreamWriter custt = File.CreateText("c:\\porozhe.txt"))
                {
                    custt.WriteLine(textBox1.Text);
                    custt.WriteLine(textBox2.Text);
                    custt.WriteLine(textBox3.Text);
                    custt.WriteLine(textBox4.Text);
                    custt.WriteLine(textBox5.Text);
                    textBox1.Text = "";
                    textBox2.Text = "";
                    textBox3.Text = "";
                    textBox4.Text = "";
                    textBox5.Text = "";                }            }
            else
            {
                using (StreamWriter custt = File.AppendText("c:\\porozhe.txt"))
                {
                    custt.WriteLine(textBox1.Text);
                    custt.WriteLine(textBox2.Text);
                    custt.WriteLine(textBox3.Text);
                    custt.WriteLine(textBox4.Text);
                    custt.WriteLine(textBox5.Text);
                    textBox1.Text = "";
                    textBox2.Text = "";
                    textBox3.Text = "";
                    textBox4.Text = "";
                    textBox5.Text = "";
                    textBox1.Focus();
                }
            }
        }
       
        //search
        private void button2_Click(object sender, EventArgs e)
        {
           string s = " ";
            using (StreamReader cust4 = File.OpenText("c:\\porozhe.txt"))
            {
                while ((s = cust4.ReadLine()) != null)
                {
                    if (s == textBox6.Text.Trim())
                    {
                        customers cust2 = new customers();
                        cust2.family = cust4.ReadLine();
                        cust2.company = cust4.ReadLine();
                        cust2.phone = Convert.ToInt32(cust4.ReadLine());
                        cust2.address = cust4.ReadLine();
                        textBox1.Text = textBox6.Text;
                        textBox2.Text =cust2.family;
                        textBox3.Text = cust2.company;
                        textBox4.Text = Convert.ToString(cust2.phone);
                        textBox5.Text = cust2.address;
                        return;
                    }
                }            }        }
 // حذف
        private void button3_Click(object sender, EventArgs e)
        {
            using (StreamWriter custt = File.AppendText("c:\\porozhe.txt"))
            {
                textBox1.Text = "";
                textBox2.Text = "";
                textBox3.Text = "";
                textBox4.Text = "";
                textBox5.Text = "";
                custt.WriteLine(textBox1.Text);
                custt.WriteLine(textBox2.Text);
                custt.WriteLine(textBox3.Text);
                custt.WriteLine(textBox4.Text);
                custt.WriteLine(textBox5.Text);
                textBox1.Text = "";
                textBox2.Text = "";
                textBox3.Text = "";
                textBox4.Text = "";
                textBox5.Text = "";
                textBox1.Focus();
            }         }        private void button5_Click(object sender, EventArgs e)
        {
            printPreviewDialog1.Document = printDocument1;
            printPreviewDialog1.ShowDialog();
        }       private void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
        {
           using(StreamReader sw5=File.OpenText("c:\\porozhe.txt"))
           string s = "" ;
           int x=10 , y=10;
           Font f1=new Font("arial black",10,FontStyle.Bold);
              
           
         
           while (( s = sw5.ReadLine()) != null)
           {
                    
               y+=20;
               e.Graphics.DrawString(s,f1,Brushes.Black,10,y);
            }
        }     /*   // ویرایش
        private void button4_Click(object sender, EventArgs e)
        {
            using (StreamWriter cust3 = File.AppendText("c:\\porozhe.txt"))
                {
                   cust3.idcustom =Convert.ToInt32 (textBox1.Text);
                     cust3.family =(textBox2.Text);
                    custt.WriteLine(textBox3.Text);
                    custt.WriteLine(textBox4.Text);
                    custt.WriteLine(textBox5.Text);
                cust3.De
                    
                    }
                }            */   
        }
    }