怎么来判断num这个值,每次都是0

protected void Button1_Click(object sender, EventArgs e)
    {            int num = 0;        if (num < 9)
        {              PictureCommand picup = new PictureCommand();
            if (picup.UpLoadIMG(this.FileUpload1))
            {
                           Response.Write(picup.OFullName.ToString() + PictureCommand.MSG.ToString());                            if (Session["imgurl"] == null )  //判断url地址集合是否有
                            {
                                Session["imgurl"] = picup.OFullName.ToString();
                            }
                            else
                            { 
                             Session["imgurl"] = picup.OFullName.ToString() + ";" + Session["imgurl"];
                            }                            this.Panel1.Controls.Clear();
                            
                            this.img((Session["imgurl"]).ToString());                                                                    num=num+1;
                            //Response.Redirect("00.aspx");
           
                    }
                    else
                    {                        Response.Write(picup.OFullName.ToString() + PictureCommand.MSG.ToString());
                                           }        }
        else
        {
            Response.Write("最多上传9张图片"); 
                    }
    }