reading different files according to user input

Hi there.

Little newbie question.

I have a program that produces a statistic report, and that needs to read 
one file or another according to user's specification via a parameter.

But there are some lines of the program where I don't know how to manage to 
go along with the choice.

E.g.:
dow not %EOF(ALFDEALHP);
(The files are either ALFDEALHP or ALFDEALHC)

In the simpler 'CHAINs' and 'READEs' I can use unelegants but effective IFs, 
but doing it around the dow would end up with something ugly.

In some other language I'd be using a reference in the beggining of the 
program for the appropriate file; and then referring to that reference 
henceforth. But my newbieness in RPG is making itself, and I''ve been over 
the infocenter for a while without good results.

Hope someone can help.

Thx.

I.-