C# Rastgele Sayı Ve Harflerden Şifre(KOD) Oluştur

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace sifrele
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}



private void button1_Click(object sender, EventArgs e)
{

string kod;
char[] harf = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','u','p','r','s','t','u','z','x','w'};
int[] sayi = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
Random r = new Random();

kod=Convert.ToString(harfler[r.Next(22)])+Convert.ToString(harfler[r.Next(22)])+Convert.ToString(sayılar[r.Next(9)])+Convert.ToString(harfler[r.Next(22)])+Convert.ToString(sayılar[r.Next(9)])+Convert.ToString(sayılar[r.Next(9)]);

label1.Text = kod;

}
}
}