private void btnSubmit_Click(object sender, EventArgs e) { if (txtQuantity.Text.All(Char.IsDigit) && (!(String.IsNullOrWhiteSpace(txtQuantity.Text)))) { GeneralMethods.UpdatePurchaseOrderTransactionQuantity(ID, Convert.ToInt32(txtQuantity.Text)); MessageBox.Show("Successfully updated!", "Success"); this.Close(); } else if (!(txtQuantity.Text.All(Char.IsDigit))) { MessageBox.Show("Quantity must only contain numbers!", "Error"); } else { MessageBox.Show("Field cannot be left empty!"); } }