获取（.）点前一个字符

string s = "123_u.jpg";
string strKzm = s.Substring(s.LastIndexOf(".")-1);//获取文件扩展名
string strImgNo1 = strKzm.Substring(0, 1);
Response.Write(strImgNo1);

计算字符串字节大小

string str = "ABC";
int s= System.Text.Encoding.GetEncoding("GB2312").GetByteCount(str);
Response.Write(s);

选择文件夹

<script type="text/javascript">

function BrowseFolder(){
try{
   var Message = "请选择文件夹";   //选择框提示信息
   var Shell = new ActiveXObject( "Shell.Application" );
   var Folder = Shell.BrowseForFolder(0,Message,0x0040,0x11);//起始目录为：我的电脑
   //var Folder = Shell.BrowseForFolder(0,Message,0); //起始目录为：桌面
   if(Folder != null){
     Folder = Folder.items();   // 返回 FolderItems 对象
     Folder = Folder.item();   // 返回 Folderitem 对象
     Folder = Folder.Path;    // 返回路径
     if(Folder.charAt(Folder.length-1) != "\\"){
       Folder = Folder + "\\";
     }
     document.all.savePath.value=Folder;
     return Folder;
   }
}catch(e){
   alert(e.message);
}
}

</script>

<input type="button" name="chosefolderbutton" value="选择" οnclick="BrowseFolder()" />

注意：提示"没有权限"

1、设置可信任站点（如：http://localhost/）

2、其次：可信任站点安全级别自定义设置中：设置   "对没有标记为安全的ActiveX控件进行初始化和脚本运行"----"启用"

上传文件

if (this.FileUpload1.HasFile)//检查是否有文件
        {
            string fullFileName = this.FileUpload1.PostedFile.FileName;
            //string fileName = fullFileName.Substring(fullFileName.LastIndexOf("\\") + 1); //图片名称
            string type = fullFileName.Substring(fullFileName.LastIndexOf(".") + 1);        //图片格式

if (type == "jpg" || type == "JPG" || type == "gif" || type == "GIF" || type == "BMP" || type == "bmp")
            {
                if (this.FileUpload1.PostedFile.ContentLength > 20 * 1024)
                {
                    Response.Write("<script>alert('上传图片必须小于20k！');</script>");
                }
                else
                {
                    string path = HttpContext.Current.Request.MapPath("~/zp/");//获取上传文件的网站目录路径

Random rand = new Random();
                    string fileName = DateTime.Now.ToString("yyyyMMddhhmm") + rand.Next(100, 999)+"."+type;
                    this.FileUpload1.SaveAs(path + fileName);

Response.Write("<script>alert('图片上传成功！');</script>");

this.Image1.ImageUrl = "~/zp/" + fileName;//显示图片
                }

}
            else
            {
                Response.Write("<script>alert('非图片类型，不允许上传！');</script>");
            }
        }
        else
        {
            Response.Write("<script>alert('必须指定文件！');</script>");
        }

}