protected void SearchButton_Click(object sender, EventArgs e)
 {
     if (BillNumberTextBox.Text == String.Empty && MobileNumberTextBox.Text == String.Empty)
     {
         MessageLabel.Text   = "Please enter bill or mobile number!";
         DueDateTextBox.Text = String.Empty;
         AmountTextBox.Text  = String.Empty;
     }
     else
     {
         if (BillNumberTextBox.Text == String.Empty &&
             !new Regex(@"(^(\+8801|8801|01|008801))[1|5-9]{1}(\d){8}$").IsMatch(MobileNumberTextBox.Text))
         {
             MessageLabel.Text      = "Please enter a Valid Bill or Mobile Number!";
             ConfirmationLabel.Text = String.Empty;
             DueDateTextBox.Text    = String.Empty;
             AmountTextBox.Text     = String.Empty;
         }
         else
         {
             if (aPatientManager.DoesBillNumberExist(BillNumberTextBox.Text) || aPatientManager.DoesMobileNumberExist(MobileNumberTextBox.Text))
             {
                 MessageLabel.Text = String.Empty;
                 Patient aPatient = aPatientManager.GetPatientByBillNumberOrMobileNumber(BillNumberTextBox.Text,
                                                                                         MobileNumberTextBox.Text);
                 ViewState["Patient"]     = aPatient;
                 BillNumberTextBox.Text   = aPatient.BillNumber;
                 MobileNumberTextBox.Text = aPatient.MobileNumber;
                 AmountTextBox.Text       = aPatient.Fee.ToString();
                 DueDateTextBox.Text      = aPatient.InvoiceDate.ToString("dd-MM-yyyy");
                 PayButton.Visible        = true;
                 ConfirmationLabel.Text   = String.Empty;
             }
             else
             {
                 MessageLabel.Text      = "Entered Bill Number Or Mobile Number Does Not Exist!";
                 DueDateTextBox.Text    = String.Empty;
                 AmountTextBox.Text     = String.Empty;
                 ConfirmationLabel.Text = String.Empty;
             }
         }
     }
 }