AppD.MerchantBank.CardService.Credit C# (CSharp) Метод

        public int Credit(string cardNumber, double amount)
        {
            int id = -1;
            if (IsValid(cardNumber))
            {
                Interlocked.Increment(ref safeInstanceCount);
                id = safeInstanceCount;
                string record = string.Format(credittransactionformatter, id, cardNumber, amount);
                log.Info(record);
            }
            return id;
        }