Delete from gridview whose checkbox is checked

 protected void Button1_Click(object sender, EventArgs e)
    {              
        foreach (GridViewRow gr in GridView1.Rows)
        {        
            var chk = gr.FindControl("CheckBox1") as CheckBox;           
            if (chk.Checked == true)
            {              
                var str12 = gr.FindControl("lblp") as Label;
                SqlConnection con = new SqlConnection("s");
                con.Open();
                string str = "delete from [order] where order_id=@order_id";
                SqlCommand cmd = new SqlCommand(str, con);
                cmd.Parameters.AddWithValue("@order_id",str12.Text);
                DataTable dt = new DataTable();
                SqlDataAdapter da = new SqlDataAdapter(cmd);
                da.Fill(dt);
                con.Close();
                GridView1.DataSource = dt;
                GridView1.DataBind();
                bind();              
            }           
        }