NCalcParser.extractString C# (CSharp) Method

    private string extractString(string text)
    {
        StringBuilder sb = new StringBuilder(text);
        int startIndex = 1; // Skip initial quote
        int slashIndex = -1;

        while ((slashIndex = sb.ToString().IndexOf(BS, startIndex)) != -1)
        {
            char escapeType = sb[slashIndex + 1];
            switch (escapeType)
            {
                case 'u':
                  string hcode = String.Concat(sb[slashIndex+4], sb[slashIndex+5]);
                  string lcode = String.Concat(sb[slashIndex+2], sb[slashIndex+3]);
                  char unicodeChar = Encoding.Unicode.GetChars(new byte[] { System.Convert.ToByte(hcode, 16), System.Convert.ToByte(lcode, 16)} )[0];
                  sb.Remove(slashIndex, 6).Insert(slashIndex, unicodeChar);
                  break;
                case 'n': sb.Remove(slashIndex, 2).Insert(slashIndex, '\n'); break;
                case 'r': sb.Remove(slashIndex, 2).Insert(slashIndex, '\r'); break;
                case 't': sb.Remove(slashIndex, 2).Insert(slashIndex, '\t'); break;
                case '\'': sb.Remove(slashIndex, 2).Insert(slashIndex, '\''); break;
                case '\\': sb.Remove(slashIndex, 2).Insert(slashIndex, '\\'); break;
                default: throw new RecognitionException("Unvalid escape sequence: \\" + escapeType);
            }

            startIndex = slashIndex + 1;

        }

        sb.Remove(0, 1);
        sb.Remove(sb.Length - 1, 1);

        return sb.ToString();
    }