protected void Button1_Click(object sender, EventArgs e)
{
    con.Open();
    SqlCommand cmd = con.CreateCommand();
    cmd.CommandType = CommandType.Text;
    cmd.CommandText = "select * from registration where email='"+ TextBox1.Text+"' and password='"+TextBox2.Text+"'";
    cmd.ExecuteNonQuery();
    DataTable dt = new DataTable();
    SqlDataAdapter da = new SqlDataAdapter(cmd);
    da.Fill(dt);
    tot = Convert.ToInt32(dt.Rows.Count.ToString());

    if (tot > 0)
    {
        if (Session["checkoutbutton"] == "yes")
        {
            Session["user"] = TextBox1.Text;
            Response.Redirect("update_order_details.aspx");
        }
        else
        {
            Session["user"] = TextBox1.Text;
            Response.Redirect("order_details.aspx");
        }

    }
    else
    {
        Label1.Text = "Invalid email or password";
    }
    con.Close();

    con.Open();
    SqlCommand cmd1 = con.CreateCommand();
    cmd1.CommandType = CommandType.Text;
    cmd1.CommandText = "select * from admin_login where username='" + TextBox1.Text + "' and password='" + TextBox2.Text + "' ";
    cmd1.ExecuteNonQuery();
    DataTable dt1 = new DataTable();
    SqlDataAdapter da1 = new SqlDataAdapter(cmd);
    da1.Fill(dt);
    i = Convert.ToInt32(dt.Rows.Count.ToString());
    if (i == 1)
    {
        Session["admin"] = TextBox1.Text;
        Response.Redirect("add_product.aspx");
    }
    else
    {
        Label1.Text = "you have entered invalid username or password";
    }
    con.Close();
}