C# 字符串操作

1.分离字母和数字

string input = "DONGFANGZHIZHU19770822";

string alpha = "";
string number = "";

foreach(char c in input) {
     if (Char.IsNumber(c))
         number += c;
     else
         alpha += c;
} 

2.截取字符

/// 截取字段
        /// </summary>
        /// <param name="str"></param>
        /// <param name="startIndex"></param>
        /// <param name="count"></param>
        /// <returns></returns>
        public string GetStringByByteLen(string str, int startIndex, int count)
        {
            int byteCount = System.Text.Encoding.Default.GetByteCount(str);
            int charCount = str.Length;
            int newByteCount = 0;
            int startPos = 0;
            int endPos = 0;
            //超过字节总数
            if (startIndex > byteCount)
            {
                return string.Empty;
            }
            //跳过前面的部分
            for (int i = 0; i < charCount; i++)
            {
                if (startPos >= startIndex)
                {
                    startPos = i;
                    break;
                }
                if (str[i] > 255)
                    startPos += 2;
                else
                    startPos += 1;
            }

            if (byteCount - startPos <= count)
            {
                if (startPos > charCount)
                {
                    return string.Empty;
                }
                else
                {
                    return str.Substring(startPos);
                }
            }
            endPos = startPos;
            for (int i = startPos; i < charCount; i++)
            {
                if (str[i] > 255)
                    newByteCount += 2;
                else
                    newByteCount += 1;
                if (newByteCount == count)
                {
                    endPos = i + 1;
                    break;
                }
                else if (newByteCount > count)
                {
                    endPos = i;
                    break;
                }
            }
            return str.Substring(startPos, endPos - startPos);
        }

 3.　　去掉html和js

  public string NoHTML(string Htmlstring) //去除HTML标记
        {
            //删除脚本
            Htmlstring = Regex.Replace(Htmlstring, @"<script[^>]*?>.*?</script>", "", RegexOptions.IgnoreCase);
            //删除HTML
            Htmlstring = Regex.Replace(Htmlstring, @"<(.[^>]*)>", "", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"([\r\n])[\s]+", "", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"-->", "", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"<!--.*", "", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(quot|#34);", "\"", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(amp|#38);", "&", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(lt|#60);", "<", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(gt|#62);", ">", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(nbsp|#160);", " ", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(iexcl|#161);", "\xa1", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(cent|#162);", "\xa2", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(pound|#163);", "\xa3", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&(copy|#169);", "\xa9", RegexOptions.IgnoreCase);
            Htmlstring = Regex.Replace(Htmlstring, @"&#(\d+);", "", RegexOptions.IgnoreCase);
            Htmlstring.Replace("<", "");
            Htmlstring.Replace(">", "");
            Htmlstring.Replace("\r\n", "");
            Htmlstring = HttpContext.Current.Server.HtmlEncode(Htmlstring).Trim();
            return Htmlstring;
        }

 4.忽略大小写

string.Equals(string1, string2, StringComparison.OrdinalIgnoreCase) 
用这个方法还不用担心比较的对象是null