Date:         Mon, 14 Oct 1996 15:09:03 -0700
Reply-To:     Chris B Long <Chris_B_Long@SANDWICH.PFIZER.COM>
Sender:       "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From:         Chris B Long <Chris_B_Long@SANDWICH.PFIZER.COM>
Organization: Pfizer Central Research, Sandwich, Kent, UK
Subject:      Re: 'Proper' use of IF-THEN-ELSE (was IF-THEN-ELSEs in a DATA
              step)

AMICELI wrote:
Chris writes:
>>This question raises a question of programming style, as well as problems
with
nested
IF statements.  In much of the user-written code that I see, there's
actually
no need
to use nested IF statements at all.  If the conditions of your various IF
statements
are mutually exclusive, why not just code them as sequential IF
statements?
For example, I often see things like:
 
if name='Fred' then do;
...
end; else if name='Mary' then do;
...
end; else if name='Ann' then do;
...
end;
 
This is logically equivalent to sequential IF statements:
 
if name='Fred' then do;
...
end;
if name='Mary' then do;
...
end;
if name='Ann' then do;
...
end;
 
but the latter doesn't involve any problems with potential stack
overflows etc.
 
<CUT>
>>>
 
Just a note from a compiler perspective. The following code:
If a=1 then do;
   %blah;
end;
else do;
   %blahblah;
end;
 
is NOT NESTED. This is merely a set of mutually exclusive conditions.
 
----------------------
 
Agreed - but I was referring to the common construct:
 
  if a=1 then do;
    <something>
  end; else if a=2 then do;
    <another thing>
  end;
 
which is different from your example, and *is* nested - the second IF
statement is nested within the ELSE clause of the first one.  The nesting
is less obvious than it should be because the indentation which is
commonly used with this sort of construct is misleading - it should
strictly be:
 
  if a=1 then do;
    <something>
  end; else if a=2 then do;
              <another thing>
            end;
 
to show that the second END is paired with the DO of the second IF
statement.  (What I regard as the aesthetic unpleasantness of this
construct is revealed when indented like this!)
 
Chris.