In Scripts, you can call a perform which in turn can do any
type of computation or calculation and return the result to
the script.

In script u write..
perform p_name using v_par1 type itcsy
                     v_par2 type itcsy
               changing v_par3 type itcsy

you can write the form p_name in the print program. 
Or in any program, but in that case u have to give the
program name also while calling the script.
perform p_name in program v_prog
               using v_par1 type itcsy
                     v_par2 type itcsy
               changing v_par3 type itcsy

v_par1 and v_par2 are passed to the form and the return
value is filled in v_par3.

you can do any type of computation using the variables
passed from the script and return the result in the changing
parameter.

Note- the type of parameter should by ITCSY.