//字元轉ASCII碼：
public static int Asc(string character)
  {
   if (character.Length == 1)
   {
    System.Text.ASCIIEncoding asciiEncoding = new System.Text.ASCIIEncoding();
    int intAsciiCode = (int)asciiEncoding.GetBytes(character)[0];
    return (intAsciiCode);
   }
   else
   {
    throw new Exception("Character is not valid.");
   }

  }

ASCII碼轉字元：

public static string Chr(int asciiCode)
  {
   if (asciiCode >= 0 && asciiCode <= 255)
   {
    System.Text.ASCIIEncoding asciiEncoding = new System.Text.ASCIIEncoding();
    byte[] byteArray = new byte[] { (byte)asciiCode };
    string strCharacter = asciiEncoding.GetString(byteArray);
    return (strCharacter);
   }
   else
   {
    throw new Exception("ASCII Code is not valid.");
   }
  }


//另一種寫法
string str="abcd";
byte[] bytetest = System.Text.Encoding.Default.GetBytes(str.ToString());
 

http://www.cnblogs.com/JoshuaDreaming/archive/2010/11/19/1882068.html