private void deleteButton_Click(object sender, EventArgs e)//deletes the customer from the system. OR shows error if the open balance is not 0 { if (!(customerNumberUpDown.Text == "0")) { if (Customer.CheckBalance(customerNumberUpDown.Text)) { Customer.DeleteCustomer(customerNumberUpDown.Text); using (StreamWriter log = File.AppendText(path)) { log.WriteLine("" + DateTime.Now + " : Customer delete: CustomerNumber = " + customerNumberUpDown.Text + ";"); this.Close(); } } else { MessageBox.Show("The balance has to be 0 before deleting a customer"); } } else { MessageBox.Show("Please choose a Customer!"); } }