Hi Sathyaraj,
HR_99S_DATE_ADD_SUB_DURATION-use this function module.
Pass importing parameters as shown above.And you will get result.
example:
Importing: IM_DATE = 31/07/2014 or(SY-DATUM)
IM_OPERATOR = ' - ' i.e substract symbol
IM_duration has a structure.
Pass IM_DURATION-DURMM = '3'.
and finally use:OIL_MONTH_GET_FIRST_LAST.
Here you will get both first and last date of the input month.
Refer this link it is very helpful:Function Module related on Date calculations - ABAP Development - SCN Wiki
thanks,
vidyasagar