OpenEuphoria

Re: Uninitialized Variables

• Posted by Derek Parnell <ddparnell at bigpond.com> Mar 23, 2002
• 468 views

> > 
> > This seems to work:
> > --------------
> > atom x,nan,inf
> > inf = 1e300 * 1e300
> > nan = inf / inf
> > 
> > x = nan
> > 
> > if x = nan then
> >     puts(1, "x is not a number\n")
> > end if
> > ? x = nan
> > ? x != nan
> > 
> 
> Actually, it doesn't.  Because
> 
> (10 = nan)
> (2.3 = nan)
> 
> will also evaluate as true and
> 
> (10 != nan)
> 
> will evaluate as false.
> 
> You need to be able to tell a non-nan from a nan...
> 

Umm, did you actually try it, Andy. Here is an expanded version:

------------------

atom x,y,nan,inf
inf = 1e300 * 1e300
nan = inf / inf

x = nan
y = 10
if x = nan then
    puts(1, "x is not a number\n")
else
    puts(1, "x is a number\n")
end if
if y = nan then
    puts(1, "y is not a number\n")
else
    puts(1, "y is a number\n")
end if
? x = nan
? x != nan
? y = nan
? y != nan
? 10 = nan
? 10 != nan

? nan
? inf
------------------

I get the following output:

x is not a number
y is a number
1
0
0
1
0
1
-nan
inf

-------------
which seems just what I'd expect.

----------
Derek.