1)判断字符串是否为空

string strValue = Request["xxx"];

if(string.IsNullOrEmpty(strValue) || strValue == "undefined")

   错误

2)查找字符串

int pos = IndexOf("IMG", System.StringComparison.OrdinalIgnoreCase);

if(pos >= 0)

   //找到

3)分割为数组

string[] split = words.Split(new char[] { ',', '.' });//返回:{"1","2","3","","4"}

string[] split = words.Split(new Char[] { ',', '.' }, StringSplitOptions.RemoveEmptyEntries);//返回:{"1","2","3","4"} 不保留空元素

string[] split = words.Split(new string[] { ",", "." }, 6, StringSplitOptions.None);//返回:{"1","2","3","","4"} 保留空元素

4)字符串比较（忽略大小写）

string A = "aBc";

string B = "AbC";

if (string.Compare(A, B, true) == 0)

    Response.Write("一致");

else

    Response.Write("不一致");