protected void showButton_OnServerClick(object sender, EventArgs e)
 {
     if (fromDateTextBox.Value.Length == 0 || toDateTextBox.Value.Length == 0)
     {
         messageLabel.Text = "<span style='color:red;font-weight:bold;font-style:italic;font-size:15px;'>From Date and To Date both should be filled.";
     }
     else
     {
         DateTime       fromDate = Convert.ToDateTime(fromDateTextBox.Value);
         DateTime       toDate   = Convert.ToDateTime(toDateTextBox.Value);
         List <Patient> patients = billManager.GetUnpaidBillInfo(fromDate, toDate);
         if (patients.Count == 0)
         {
             messageLabel.Text = "<span style='color:red;font-weight:bold;font-style:italic;font-size:15px;'>No Information found</span>";
         }
         else
         {
             unpaidBillReportGridView.DataSource = patients;
             unpaidBillReportGridView.DataBind();
         }
     }
 }