how do we download sharepoint files programatically with save dialog box

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C#5.0

SharePoint2010

Hi,
In my application i wanted to download the sharepoint file programatically in a webpart.
for that i have used below code.It is getting downloaded but no save dialog box is coming , page is refreshing and file is getting downloaded, no intimations.

HttpWebRequest request;
         HttpWebResponse response = null;
         string pathUser =       Environment.GetFolderPath(Environment.SpecialFolder.Personal);
         string pathDownload = Path.Combine(pathUser, "Downloads");
         request = (HttpWebRequest)WebRequest.Create(strURL);
         request.Credentials = System.Net.CredentialCache.DefaultCredentials;
         request.Timeout = 20000;
         request.AllowWriteStreamBuffering = true;
         response = (HttpWebResponse)request.GetResponse();
         Stream s = response.GetResponseStream();

         if (!Directory.Exists("C:\\Users\\Administrator\\Downloads"))
         {
             Directory.CreateDirectory(@"C:\Users\Administrator\Downloads");
         }

         string aFilePath = "C:\\Users\\Administrator\\Downloads" + "\\" + strFileName;
         FileStream fs = new FileStream(aFilePath, FileMode.Create);
         byte[] read = new byte[256];
         int count = s.Read(read, 0, read.Length);
         while (count > 0)
         {
             fs.Write(read, 0, count);
             count = s.Read(read, 0, read.Length);
         }
        fs.Close();
         s.Close();
         response.Close();

So how can we put save dialog box here?

Thanks
Ginnas