C#获得字符串首字符字母（大写）

/// <summary>
/// 获得字符串首字符字母（大写）；
/// </summary>
/// <param name="cnChar"></param>
/// <returns></returns>
public string GetStringFirstSpell(string cnChar)
{
//除字母、数字、汉字以外的返回"*"
var result = "*";

if (string.IsNullOrEmpty(cnChar.Trim()))
return result;

cnChar = cnChar.Trim().Substring(0, 1);
byte[] arrCn = Encoding.Default.GetBytes(cnChar);

//首字为字符,占一个字节
if (arrCn.Length <= 1)
{
//大写英文字母
if ((short)arrCn[0] >= 65 && (short)arrCn[0] <= 90)
return cnChar;

//小写英文字母
if (arrCn[0] >= 97 && arrCn[0] <= 122)
return Encoding.Default.GetString(new byte[] { (byte)((short)arrCn[0] - 32) });

//数字
switch (cnChar)
{
case "1":
result = "Y";
break;
case "2":
result = "E";
break;
case "3":
case "4":
result = "S";
break;
case "5":
result = "W";
break;
case "0":
case "6":
result = "L";
break;
case "7":
result = "Q";
break;
case "8":
result = "B";
break;
case "9":
result = "J";
break;
}
return result;
}
//首字为汉字,占两个字节
else
{
int area = (short)arrCn[0];
int pos = (short)arrCn[1];
int code = (area << 8) + pos;
int[] areacode = { 45217, 45253, 45761, 46318, 46826, 47010, 47297, 47614, 48119, 48119, 49062, 49324, 49896, 50371, 50614, 50622, 50906, 51387, 51446, 52218, 52698, 52698, 52698, 52980, 53689, 54481 };
for (int i = 0; i < 26; i++)
{
int max = 55290;
if (i != 25) max = areacode[i + 1];
if (areacode[i] <= code && code < max)
{
return Encoding.Default.GetString(new byte[] { (byte)(65 + i) });
}
}
return result;
}
}