How to get start and end dates of last quarter

private void button1_Click(object sender, EventArgs e)
        {
            DateTime startDate = default(DateTime);
            DateTime endDate = default(DateTime);
            string lastQuarter = GetLastQuarterDates(DateTime.Now.Month);
            SetLastQuarterDates(out startDate, out endDate, lastQuarter);
            label1.Text = Convert.ToString(startDate);
            label2.Text = Convert.ToString(endDate);
        }  

private void SetLastQuarterDates(out DateTime startDate, out DateTime endDate, string quarter)
        {
            int startMonth = 0;
            int startYear = DateTime.Now.Year;
            int startDay = 1;
            int endMonth = 0;
            int endYear = DateTime.Now.Year;
            int endDay = 31;

            switch (quarter)
            {
                case "Q1":
                    startMonth = 1;
                    endMonth = 3;
                    endDay = 30;
                    break;

                case "Q2":
                    startMonth = 4;
                    endMonth = 6;
                    break;

                case "Q3":
                    startMonth = 7;
                    endMonth = 9;
                    endDay = 30;
                    break;

                case "Q4":
                    startMonth = 10;
                    startYear = DateTime.Now.Year - 1;
                    endMonth = 12;
                    endYear = DateTime.Now.Year - 1;
                    break;
            }

            startDate = new DateTime(startYear, startMonth, startDay);
            endDate = new DateTime(endYear, endMonth, endDay);
        }

        private string GetLastQuarterDates(int month)
        {
            string quarter = string.Empty;

            if (month >= 1 && month <= 3)
            {
                quarter = "Q4";
            }
            if (month >= 4 && month <= 6)
            {
                quarter = "Q1";
            }
            if (month >= 7 && month <= 9)
            {
                quarter = "Q2";
            }
            if (month >= 10 && month <= 12)
            {
                quarter = "Q3";
            }

            return quarter;
        }

// ----------------------------------------------------------------------
public static void DaysOfPastQuarter( DateTime moment )
{
  // example of fiscal year, which starts at October
  TimeCalendar calendar = new TimeCalendar( new TimeCalendarConfig { YearBaseMonth = YearMonth.October } );
  Quarter currentQuarter = new Quarter( moment, calendar );
  Quarter pastQuarter = currentQuarter.GetPreviousQuarter();

  Console.WriteLine( "Start: " + pastQuarter.FirstDayLast );
  Console.WriteLine( "End: " + pastQuarter.LastDayStart );
} // DaysOfPastQuarter