C#下提取汉字首字的拼音首字母并兼容英文与数字

 public static string CVT(string str)
        {
            if (str.CompareTo("吖") < 0)
            {
                string s=str.Substring(0,1).ToUpper();
                if (char.IsNumber(s, 0))
                {
                    return "0";
                }
                else
                {
                    return s;
                }

            }else if (str.CompareTo("八") < 0)
            {
                return "A";
            }
            else if (str.CompareTo("嚓") < 0)
            {
                return "B";
            }
            else if (str.CompareTo("咑") < 0)
            {
                return "C";
            }
            else if (str.CompareTo("妸") < 0)
            {
                return "D";
            }
            else if (str.CompareTo("发") < 0)
            {
                return "E";
            }
            else if (str.CompareTo("旮") < 0)
            {
                return "F";
            }
            else if (str.CompareTo("铪") < 0)
            {
                return "G";
            }
            else if (str.CompareTo("讥") < 0)
            {
                return "H";
            }
            else if (str.CompareTo("咔") < 0)
            {
                return "J";
            }
            else if (str.CompareTo("垃") < 0)
            {
                return "K";
            }
            else if (str.CompareTo("嘸") < 0)
            {
                return "L";
            }
            else if (str.CompareTo("拏") < 0)
            {
                return "M";
            }
            else if (str.CompareTo("噢") < 0)
            {
                return "N";
            }
            else if (str.CompareTo("妑") < 0)
            {
                return "O";
            }
            else if (str.CompareTo("七") < 0)
            {
                return "P";
            }
            else if (str.CompareTo("亽") < 0)
            {
                return "Q";
            }
            else if (str.CompareTo("仨") < 0)
            {
                return "R";
            }
            else if (str.CompareTo("他") < 0)
            {
                return "S";
            }
            else if (str.CompareTo("哇") < 0)
            {
                return "T";
            }
            else if (str.CompareTo("夕") < 0)
            {
                return "W";
            }
            else if (str.CompareTo("丫") < 0)
            {
                return "X";
            }
            else if (str.CompareTo("帀") < 0)
            {
                return "Y";
            }
            else if (str.CompareTo("咗") < 0)
            {
                return "Z";
            }
            else
            {
                return "0";
            }

         
        }