a difficult control input question

some_one

htp://s290,photobucket,com/albums/ll279/transgalactic/?action=view&current=IMG_8838,jpg

the main problem comes when in one input i need to divide the number by 2
(subtract a zero from the original input)

while in other control input i need to multiply by two
(which meens to add a zero to the original input)

i dont know how to delete or add an output
when i have a certain control input

the number of outputs is constant

what should i do??