Can I assign value to import parameter in Function Module? How?

Hi Experts,

Function Module " Ztest "

import num = num

export res = res.

in the function module, I am checking the condition as following:

if num is initial.

num = 100.

endif.

but, Syntax error is occuring that

"NUM cant be changed".

I want to assign new value to num like 200.

How do I assign ?

Please help me out.

thanks in advance.

regards

Sekhar