to test whether line-segments cross - what am I doing wrong?

[john n <johnnagelson@yahoo.co.uk>]

Newbie question... I'm trying to write a routine to test for whether two
unit-length line-segments cross.

I'm OK with the maths, but am having problems implementing it!
All I need to do is store either 0 or 1 in the variable 'cross', according
to whether the line-segments cross or do not cross.

But I keep getting "%1 = cross-1", and then when I run it again with the
same input, I get "%2 = 31".
There's surely a simple reason for this, obvious to any non-newbie, but I
haven't worked out what it is!

If the two line-segments miss each other by less than 10^-5 units, I count
them as crossing.

Code attached below.

Many thanks in advance for any help!

Regards,

John N

http://www.nabble.com/file/p11204331/cross-tester.gp cross-tester.gp 
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