Service programs, procedures, not sure what to do

I have a code file that we use for lots of things like customer xxxxxx
requires printed invoice, print special pick ticket format for store, etc.



The code file is keyed by group#, code. It has several fields, including
one numeric.



We always code chains and updates in every program. I'd like to be able to
do something like this instead:



If checkCodeExists(145'INVOICES');

Dostuff;

Endif;



Or



Next# = GetNextNumber(155:'INVOICE_NUMBER');



This program should chain, add 1, update, return the value.



I tried to code the PR/PI in my first RPG and it says I can't return a
value. Do I need something different? Sorry I'm so vague. I'm still not
where I need to be on procedures/service programs, etc.



Thanks, Jack