ANSI文本格式读写

StreamReader sr = new StreamReader("yourFilePath", Encoding.Default);
string strBody = sr.ReadToEnd();
sr.Close();

写文件
StreamWriter sw = new StreamWriter("yourFilePath", false, Encoding.Default);
sw.Write("中文ABC");
sw.Close();

//字符Unicode

string s = "abCDlks";

//字符转Default(//8位无编码整数)

byte[] buffer = Encoding.Default.GetBytes(s);

//Default转Utf-8

string sU8 = Encoding.UTF8.GetString(buffer);

C# 字符转ASCII码，ASCII码转字符

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码转字符：

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

}