generate เดือนไม่ขึ้นช่วยดูโค้ดกับรูปที่แนบมาให้ทีครับ

public static DateTime NextM(DateTime dateT)
        {
            if (dateT.Day != DateTime.DaysInMonth(dateT.Year, dateT.Month))
            {
                dateT = dateT.AddMonths(1);
                return new DateTime(dateT.Year, dateT.Month, DateTime.DaysInMonth(dateT.Year, dateT.Month));
            }
            else
            {
                dateT = dateT.AddDays(1).AddMonths(1).AddDays(-1);
                return new DateTime(dateT.Year, dateT.Month, DateTime.DaysInMonth(dateT.Year, dateT.Month));
            }
        }

        public void GenTable()
        {
            string STARTPAY_PERIOD = dsMain.DATA[0].STARTPAY_PERIOD;
            decimal PERIOD_INSTALLMENT = dsMain.DATA[0].PERIOD_INSTALLMENT;
            decimal PRINCIPAL_BALANCE = dsMain.DATA[0].PRINCIPAL_BALANCE;
            decimal PERIOD_PAYMENT = dsMain.DATA[0].PERIOD_PAYMENT;
            decimal CONTINT_RATE = dsMain.DATA[0].CONTINT_RATE;
            decimal INT_RATE = (CONTINT_RATE / 100);
            decimal prnpay_amt = 0;
            decimal intpay_amt = 0;
            int intday = 0;

            DateTime dateT = DateTime.ParseExact(STARTPAY_PERIOD, "yyyyMM", WebUtil.TH);
            dateT = new DateTime(dateT.Year, dateT.Month, DateTime.DaysInMonth(dateT.Year, dateT.Month));
            decimal an_year = dsMain.DATA[0].an_year;