C#关于日期月天数和一年有多少周及某年某周时间段的计算

/// <summary>

        /// 当前月有多少天

        /// </summary>

        /// <param name="y"></param>

        /// <param name="m"></param>

        /// <returns></returns>

        public static int HowMonthDay(int y, int m)

        {

            int mnext;

            int ynext;

            if (m < 12)

            {

                mnext = m + 1;

                ynext = y;

            }

            else

            {

                mnext = 1;

                ynext = y + 1;

            }

            DateTime dt1 = System.Convert.ToDateTime(y + "-" + m + "-1");

            DateTime dt2 = System.Convert.ToDateTime(ynext + "-" + mnext + "-1");

            TimeSpan diff = dt2 - dt1;

            return diff.Days;

        }

        /**//// <summary>

        /// 得到一年中的某周的起始日和截止日

        /// 年 nYear

        /// 周数 nNumWeek

        /// 周始 out dtWeekStart

        /// 周终 out dtWeekeEnd

        /// </summary>

        /// <param name="nYear"></param>

        /// <param name="nNumWeek"></param>

        /// <param name="dtWeekStart"></param>

        /// <param name="dtWeekeEnd"></param>

        public static void GetWeek(int nYear, int nNumWeek, out   DateTime dtWeekStart, out   DateTime dtWeekeEnd)

        {

            DateTime dt = new DateTime(nYear, 1, 1);

            dt = dt + new TimeSpan((nNumWeek - 1) * 7, 0, 0, 0);

            dtWeekStart = dt.AddDays(-(int)dt.DayOfWeek + (int)DayOfWeek.Monday);

            dtWeekeEnd = dt.AddDays((int)DayOfWeek.Saturday - (int)dt.DayOfWeek + 1);

        }

        /**//// <summary>

        /// 求某年有多少周

        /// 返回 int

        /// </summary>

        /// <param name="strYear"></param>

        /// <returns>int</returns>

        public static int GetYearWeekCount(int strYear)

        {

            string returnStr = "";

            System.DateTime fDt = DateTime.Parse(strYear.ToString() + "-01-01");

            int k = Convert.ToInt32(fDt.DayOfWeek);//得到该年的第一天是周几

            if (k == 1)

            {

                int countDay = fDt.AddYears(1).AddDays(-1).DayOfYear;

                int countWeek = countDay / 7 + 1;

                return countWeek;

            }

            else

            {

                int countDay = fDt.AddYears(1).AddDays(-1).DayOfYear;

                int countWeek = countDay / 7 + 2;

                return countWeek;

            }

        }

        /**//// <summary>

        /// 求当前日期是一年的中第几周

        /// </summary>

        /// <param name="date"></param>

        /// <returns></returns>

        public static int WeekOfYear(DateTime curDay)

        {

            int firstdayofweek = Convert.ToInt32(Convert.ToDateTime(curDay.Year.ToString() + "- " + "1-1 ").DayOfWeek);

            int days = curDay.DayOfYear;

            int daysOutOneWeek = days - (7 - firstdayofweek);

            if (daysOutOneWeek <= 0)

            {

                return 1;

            }

            else

            {

                int weeks = daysOutOneWeek / 7;

                if (daysOutOneWeek % 7 != 0)

                    weeks++;

                return weeks + 1;

            }

        }

转载于:https://www.cnblogs.com/dogxuefeng/archive/2013/06/08/3126902.html