private void grid_view()
{
   string s=ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
   string sel = "select * from TableName";
   SqlConnection con = new SqlConnection(s);
   SqlCommand cmd = new SqlCommand(sel, con);
   SqlDataAdapter sda = new SqlDataAdapter(cmd);
   DataSet ds = new DataSet();
   sda.Fill(ds);
   GridView1.DataSource = ds;
   GridView1.DataBind();
}