Hi
About Approximate operator, you can go to tcode 'ABAPDOCU', searching CO,CN,CA etc...each of them have example there.
And recursive function,
Say here is a FM,
FUNCTION recursive_get_number.
*import im_num type i.
*export ex_num type i.
ex_num = im_num + 1.
IF ex_num GE 100.
EXIT.
ELSE.
CALL FUNCTION recursive_get_number
EXPORTING
im_num = ex_num
IMPORTING
ex_num = ex_num.
ENDIF.
ENDFUNCTION.
When you call this function from outside with importing parameter '1', then will return you 100.
regards,
Archer.