How to Upload and display image and show full path of image

using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.IO;
public partial class _Default : System.Web.UI.Page
{
    //System.String name, ext;
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string fileExtension = Path.GetExtension(FileUpload1.PostedFile.FileName.ToString());

        if (FileUpload1.HasFile)
        {
            if (fileExtension == ".jpg" || fileExtension == ".png")
            {
                string a = Server.MapPath("~/image/");
                FileUpload1.SaveAs(a + FileUpload1.FileName);


                Image1.ImageUrl = "~/image/" + FileUpload1.FileName;
                Label1.Text = FileUpload1.FileName;
                Label3.Text="~/image/" + FileUpload1.FileName;


            }

            else
            {

                Label2.Text = "invalid file extension";





             //   Label1.Text = "pls upload a file";


            }





        }

    }
}