string str = "hello";

             byte[] array = new byte[];

             array = System.Text.Encoding.ASCII.GetBytes(str); //把str的每个字符转换成ascii码

             int asciicode1 = (short)(array[]);//h 的ascii码

             int asciicode2 = (short)(array[]);//e 的ascii码

             int asciicode3 = (short)(array[]);//l 的ascii码

             int asciicode4 = (short)(array[]);//l 的ascii码

             int asciicode5 = (short)(array[]);//o 的ascii码

             int asciicode = ;

             for (int i = ; i < array.Length; i++)

             {

                 asciicode += array[i];//str 的ascii码

             }

 byte[] array = new byte[];

 array[] = (byte)(Convert.ToInt32());//ASCII码强制转换二进制

 string ret=Convert.ToString(System.Text.Encoding.ASCII.GetString(array));