RE: Two reade loops: which one preferred ?

Ah, the great 'how to read a file' discussion.  Nothing beats a
classic.

Here's my .02.  RPG offers a very clean way to do this.  Its called
the cycle (ducking, running, hiding), but if you want to control
it yourself you have to decide which is worse - data file access
in two places (double the opportunities to screw something up
under maintenance) or loop exit checking in two places (offends
purists aesthetic sensibilities).  Neither is 100% satisfactory. I 
would be surprised if either turned out to be significantly
superior in performance.  

For clarity and maintenance, it is probably best to pick one
as a shop standard and stick with it.  Then everyone knows
what to look out for.

That said, I prefer:

   Setll key format;
   Dou %eof;
   Reade key format;
   If not %eof;
       do stuff;
   Endif;
   Enddo;

Because it allows easy skipping of records and quitting:

   Setll key format;
   Dou %eor
   Reade key format;
   If not %eof;
       if don't want this record;
         iter;
       endif;
       if all done for some other reason;
        leave;
      endif;
   Endif;
   Enddo;

Although this loop has one entrance and one exit, there
are those who would say it is not structured unless it
is re-written to have 25 endifs at the bottom.  Pfuie.