[C#][擴充方法] 取得日期的統一發票期別

        /// <summary> 傳入日期傳出發票期別的兩個數字 [1 2] [3 4]...</summary>
&nbsp; &nbsp; &nbsp; &nbsp; /// <param name="datetime">要判斷的日期</param>
&nbsp; &nbsp; &nbsp; &nbsp; /// <returns> 整數陣列[0]期別第一個月份 [1]期別第二個月份 </returns>
&nbsp; &nbsp; &nbsp; &nbsp; public static int[] ToInvoiceMonthRange(this DateTime datetime)
&nbsp; &nbsp; &nbsp; &nbsp; {
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //2 4 6 8...->餘0 ->[2-1,2][4-1,4]
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //1 3 5 7...->餘1 ->[1,1+1][3,3+1]
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return (datetime.Month % 2) == 0
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ? new int[] { datetime.Month - 1, datetime.Month }
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; : (datetime.Month % 2) == 1
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ? new int[] { datetime.Month, datetime.Month+1 }
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; : new int[] { 0, 0 };
&nbsp; &nbsp; &nbsp; &nbsp; }