gridview issue in asp.net

See more:

C#

ASP.NET

how to differentiate checked/unchecked checkboxes in gridview .if i select 19 records it's ok.if i am trying to select 20 record that's time remaining uncheck records checkboxes will be disabled.

i am using this code

int j = 0;
                    for (int i = 0; i < gridlob.Rows.Count; i++)
                    {

                        //finding checkbox in GridView
                        CheckBox cbx = (CheckBox)gridlob.Rows[i].FindControl("chkReimbursable");
                        //CheckBox not null
                        if (cbx != null)
                        {
                            //if CheckBox Checked

                            if (cbx.Checked)
                            {

                                j++;

                                //add your logic here.
                                //this is for example to get first column values of selected CheckBox
                                //string firstColumnValue = gridlob.Rows[i].Cells[0].Text;
                                //Response.Write(firstColumnValue);

                                if (j > 19)
                                {
                                    Page.ClientScript.RegisterStartupScript(this.GetType(), "ErrorAlert", "alert('Please select 19 lobs only');", true);
                                }


                            }
                        }

                    }

Please share your's information