hi,
i forget Tdate in declaration..
TDATE LIKE SY-DATUM,
Tdate ,Rdate also date our requirement purpose we declared...
In ur selection screen ur declared Date like this 08.2013 to 10.2013..
Then RDATE or SDATE Both is same... 01.08.2013
Tdate is 01.10.2013 After Using this function module RE_LAST_DAY_OF_MONTH
u will get last day of the month.. After Change the TDATE is EDATE..Noe EDATE is 31.10.2013...