c#自定义函数-计算某年某周的周几的日期

        //计算某年某周的周几的日期
        //参数dweek取值是1-53，表示第几周
        //参数dweekday取值是1-7，表示周一到周日
      private DateTime DateOfWeek(int dyear, int dweek, int dweekday)
        {
            string firstdayofyear = dyear.ToString() + "-01-01";
            DateTime firstday = Convert.ToDateTime(firstdayofyear);
            int weekday = (int)firstday.DayOfWeek;
            if (weekday == 0) weekday = 7;
            DateTime dt = firstday.AddDays((dweek - 2) * 7 + weekday + dweekday - 1);
            return dt;
        }