"Reprint" Some extensions to C#datetime, calculate the first day of the week, the last day

/// <summary>
    /// Some extensions of DateTime
    /// </ summary>
    public class DateTime2
    {
        /// <summary>
        /// get the first day of the week (take Sunday as the first day)
        /// </ summary>
        /// <param name = "datetime"> </ param>
        /// <returns> </ returns>
        public DateTime GetWeekFirstDaySun (DateTime datetime)
        {
            // Sunday is the first day
            int weeknow = Convert.ToInt32 (datetime.DayOfWeek);
            int daydiff = (-1) * weeknow;

            // First day of the week
            string FirstDay = datetime.AddDays (daydiff) .ToString ("yyyy-MM-dd");
            return Convert.ToDateTime (FirstDay);
        }

        /// <summary>
        /// Get the first day of the week (take Monday as the first day)
        /// </ summary>
        /// <param name = "datetime"> </ param>
        /// <returns> </ returns>
        public DateTime GetWeekFirstDayMon (DateTime datetime)
        {
            // Monday is the first day
            int weeknow = Convert.ToInt32 (datetime.DayOfWeek);

            // Because Monday is the first day, if you want to judge weeknow equal to 0, you need to push forward 6 days.
            weeknow = (weeknow == 0? (7-1): (weeknow-1));
            int daydiff = (-1) * weeknow;

            // First day of the week
            string FirstDay = datetime.AddDays (daydiff) .ToString ("yyyy-MM-dd");
            return Convert.ToDateTime (FirstDay);
        }

        /// <summary>
        /// get the last day of the week (take Saturday as the last day)
        /// </ summary>
        /// <param name = "datetime"> </ param>
        /// <returns> </ returns>
        public DateTime GetWeekLastDaySat (DateTime datetime)
        {
            // Saturday is the last day
            int weeknow = Convert.ToInt32 (datetime.DayOfWeek);
            int daydiff = (7-weeknow)-1;

            // last day of the week
            string LastDay = datetime.AddDays (daydiff) .ToString ("yyyy-MM-dd");
            return Convert.ToDateTime (LastDay);
        }

        /// <summary>
        /// get the last day of the week (take Sunday as the last day)
        /// </ summary>
        /// <param name = "datetime"> </ param>
        /// <returns> </ returns>
        public DateTime GetWeekLastDaySun (DateTime datetime)
        {
            // Sunday is the last day
            int weeknow = Convert.ToInt32 (datetime.DayOfWeek);
            weeknow = (weeknow == 0? 7: weeknow);
            int daydiff = (7-weeknow);

            // last day of the week
            string LastDay = datetime.AddDays (daydiff) .ToString ("yyyy-MM-dd");
            return Convert.ToDateTime (LastDay);
        }
    } 

Original link: http://blog.csdn.net/joyhen/article/details/9179763

"Reprint" Some extensions to C#datetime, calculate the first day of the week, the last day