public void AddPaymentToTransaction() { DataManager dataManager = new DataManager(connectionString); string transactionID = TransIDTextBox.Text; string paymentDate = DateTime.Today.ToShortDateString(); double paymentAmount = Convert.ToDouble(PaymentTextBox.Text); double newPrincipal; if (currentPrincipal == 0) { newPrincipal = principal - paymentAmount; } else { newPrincipal = currentPrincipal - paymentAmount; } dataManager.InsertNewPayment(transactionID, paymentDate, paymentAmount.ToString(), newPrincipal.ToString()); if (newPrincipal == 0) { dataManager.UpdatePawnToClosed(transactionID); } }