Another Number of Days in Month Function

CREATE function fDaysInMonth (@dtIn datetime)
returns int
as
begin
/*
For SQL Server
Description:
   Function designed to calculate the number days in a month.
*/
DECLARE @strDayOne as CHAR(20)

--Get the first day of the month of the date passed.
SET @strDayOne = CAST(DATEPART(yyyy,@dtIn) AS CHAR(4)) + '-' + CAST(DATEPART(mm,@dtIn) AS CHAR(2)) + '-01'

--Return one month forward less one day then extract the last day of the month as number of days.
RETURN DATEPART(dd,DATEADD(m,1,@strDayOne)-1)

end