Asp. NET uploading pictures using File Upload controls

aspx code<%@ page language= "C #" autoeventwireup= "true" codefile= "Default.aspx.cs" inherits= "_default"%>
<! DOCTYPE HTML Public"-//W3C//DTD XHTML 1.0 transitional//en" "HTTP://WWW.W3.ORG/TR/XHTML1/DTD/XHTML1-TRANSITIONAL.DTD"> "http://www.w3.org/1999/xhtml"> "Server"> <title> Uploading Images </title> "Form1"runat="Server"> <div> <asp:fileupload id="FileUpload1"runat="Server"/> <asp:button id="Btnfileupload"runat="Server"text="Upload"onclick="Btnfileupload_click"/> </div> </form> </body> 
CS Codeusing System;
UsingSystem.Configuration; usingSystem.Data; usingSystem.Linq; usingsystem.web; usingSystem.Web.Security; usingSystem.Web.UI; usingSystem.Web.UI.HtmlControls; usingSystem.Web.UI.WebControls; usingSystem.Web.UI.WebControls.WebParts; usingSystem.Xml.Linq;  Public Partial class_default:system.web.ui.page {protected voidPage_Load (Objectsender, EventArgs e) {        }      protected voidBtnfileupload_click (Objectsender, EventArgs e) {Boolean FileOK=false; //get the uploaded file name        stringFileName = This.          Fileupload1.filename; //Get Physical pathString Path = Server.MapPath ("~/images/"); //determine if the upload control uploads a file        if(fileupload1.hasfile) {//Determine if the extension of the uploaded file is an allowed extension of ". gif", ". png", ". jpeg", ". jpg", ". BMP "String fileextension =System.IO.Path.GetExtension (fileName).              ToLower (); String[] Extensions= {". gif",". PNG",". JPEG",". jpg",". bmp"};  for(inti =0; i < extensions.length; i++)              {                  if(FileExtension = =Extensions[i]) {FileOK=true; }              }          }          //if the upload file name extension is allowed, save the file in the directory specified on the server        if(FileOK) {Try              {                   This. FileUpload1.PostedFile.SaveAs (path +fileName); MessageBox ("File Upload Complete"); }              Catch(Exception ex) {MessageBox ("The file cannot be uploaded because:"+Ex.              Message); }          }          Else{MessageBox ("This type of file cannot be uploaded"); }      }        protected voidMessageBox (stringstr) {Page.ClientScript.RegisterStartupScript (Page.gettype (),"message","<script language= ' javascript ' Defer>alert ('"+str+"');</script>"); }  }