压缩 将字符转成16进制 并压缩一半

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

namespace WindowsFormsApplication4
{
    public partial class Form1 : Form
    {
          public string StringToHex(string str)
          {
              //str = str.Trim();
              //int i;
             /* char[] values = str.ToCharArray();
              foreach (char aa in values)
              {
                  aa = aa - 30;
              }
               */
              int i;
              byte[] ByteFoo = System.Text.Encoding.Default.GetBytes(str);//将输入的字符转成16进制
              string TempStr = "";
              byte[] aa = new byte[ByteFoo.Length/2];
              byte[] bb = new byte[ByteFoo.Length/2];
              byte[] cc = new byte[ByteFoo.Length/2];
              byte[] dd = new byte[ByteFoo.Length/2];
              for (i=0;i<ByteFoo.Length/2;i++)
              {
                  aa[i] = (byte)(ByteFoo[2 * i] << 4);//将奇数字节转成BCD码 31---》1
                  bb[i] = (byte)(ByteFoo[2 * i + 1] << 4);
                  dd[i] = (byte)(bb[i] >> 4);// 将偶数字节转成BCD码
                  cc[i] = (byte)(aa[i] | dd[i]);//合并
              }
              foreach (byte b in cc)
              {
                  //(b << 4);
                  TempStr += b.ToString("X"); //X表示十六进制显示
              }
             
              return TempStr;
          }
        
        /// <summary>
        ///将2n字符压缩成n个字符
        ///str 5678
        ///ByteFoo 35 36 37 38
        ///aa 50 70
        ///bb 60 80
        ///dd 06 08
        ///cc 56 78
        /// </summary>
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string str;
            string bb;
            str = textBox1.Text;
            //bb = ConvertToHex(str);
            bb = StringToHex(str);
            textBox3.Text = bb;
        }
    }
}