[gecode-users] Slight modification of examples/money.cc that reveals a bug

[Olof Sivertsson]

Hello,

I think I've stumbled across a bug that is quite easy to reproduce by doing
a slight modification of examples/money.cc.

Without modification running examples/money will print:
 9 5 6 7 1 0 8 2
which is the values of the letters in the array [s,e,n,d,m,o,r,y].

Now let's force s = 9 by adding the following to Money(const Options& opt)
 post(this, s == 9);

Recompile & rerun:
> make compileexamples
> examples/money
...
 9 5 6 7 1 0 8 2

No change - it works like it should. But now let's do a small change, and
instead post the following constraint:
 post(this, 9 == s);

If we recompile and rerun it now we get no solution, so somethings broken. I
bet it's a sign error since if we change it to:
 post(this, -9 == s);
it works!

Hopefully this will lead you straight to the bug and a trivial fix.

Cheers,
Olof
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