C#字节数组与字符串转换

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;

namespace 垃圾1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            byte[] a = new byte[] { 0x43,0x51,0x30,0x30,0x30,0x30,0x30,0x31 };
            textBox1.Text = System.Text.ASCIIEncoding.UTF8.GetString(a);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string str = "CQ000001";
            byte[] b = new byte[];
            b = System.Text.ASCIIEncoding.UTF8.GetBytes(str);
            for (int i = ; i < ; i++)
            {
                textBox2.Text += b[i].ToString("x02");
            }
        }

    }
}