C#索引超出了数组界限问题 - .NET技术 / C#

byte[] data1 = new byte[25];
  string str = " ";
  switch (Data1[3])
  {
  case 0x20:
  str = "1";
  str += str;
  break;
  case 0x21:
  str = "2";
  str += str;
  break;
  case 0x22:
  str = "3";
  str += str;
  break;
  case 0x23:
  str = "4";
  str += str;
  break;
  case 0x24:
  str = "5";
  str += str;
  break;
  case 0x25:
  str = "6";
  str += str;
  break;
  case 0x26:
  str = "7";
  str += str;
  break;
  case 0x27:
  str = "8";
  str += str;