C#中时间的减法求出时间差

1.取某月的最后一天

   //1.使用算出该月多少天，年+月+加上多少天即可,举例取今天最后一天
        private static void GetLastDateForMonth(DateTime dtStart,out DateTime dtEnd)
        {
            int dtYear, dtMonth;
            //dtStart = DateTime.Now;
            dtYear = dtStart.Year;
            dtMonth = dtStart.Month;
            int MonthCount = DateTime.DaysInMonth(dtYear, dtMonth);
            dtEnd = Convert.ToDateTime(dtYear.ToString() + "-" + dtMonth.ToString() + "-" + MonthCount);

        }

      private static void GetLastDateForMonth(DateTime dtStart, out DateTime dtEnd)
        {
            int dtYear, dtMonth;
            DateTime dtStart2= dtStart.AddMonths(1);
            dtYear = dtStart2.Year;
            dtMonth = dtStart2.Month;
            dtEnd = Convert.ToDateTime(dtYear.ToString() + "-" + dtMonth.ToString() + "-" + "1").AddDays(-1);

        }

2.时间差的计算TimeSpan

 DateTime dt1 = new DateTime(2021, 5, 18, 14, 23,22);
            DateTime dt2 = DateTime.Now;
             TimeSpan ts = dt1.Subtract(dt2);
            Console.WriteLine($"相差{ts.Days}天{ts.Hours}小时{ts.Minutes}分钟{ts.Seconds}秒");
            Console.ReadKey();