First and Last Day of Week Month and Year

        //Calculates first day of year
        public static DateTime firstDayOfYear(DateTime dateTime)
        {
            DateTime result;
            result = dateTime.AddDays(-(dateTime.Day - 1));
            result = result.AddMonths(-(dateTime.Month - 1));
            return result;
        }

        //Calculates last day of year
        public static DateTime lastDayOfYear(DateTime dateTime)
        {
            DateTime result;
            result = dateTime.AddYears(1);
            result = result.AddMonths(-(dateTime.Month-1));
            result = result.AddDays(-(dateTime.Day));
            return result;
        }

        //Calculates first day of month
        public static DateTime firstDayOfMonth(DateTime dateTime)
        {
            DateTime result;
            result=dateTime.AddDays(-(dateTime.Day-1));
            return result;
        }

        //Calculates last day of month
        public static DateTime lastDayOfMonth(DateTime dateTime)
        {
            DateTime result;
            result = dateTime.AddMonths(1);
            result = result.AddDays(-(dateTime.Day));           
            return result;
        }

        //Calculates first day of week
        public static DateTime firstDayOfWeek(DateTime dateTime)
        {
            DateTime result;
            result = dateTime.AddDays(-(Convert.ToInt32(dateTime.DayOfWeek)-1));
            return result;
        }

        //Calculates last day of week
        public static DateTime lastDayOfWeek(DateTime dateTime)
        {
            DateTime result;
            result = dateTime.AddDays((7-Convert.ToInt32(dateTime.DayOfWeek)));
            return result;
        }