In the original code, the slope is 0 for both horizontal and vertical lines, so you would have to first check for zero slope, then check for a stationary abscissa :-) to differentiate between horizontal and vertical. Personally, I would have made the slope undef for a vertical line, but it wouldn't make much difference in amount of coding effort.

I like the approach of LanX taking this out of the Cartesian setting and into vector notation; it generalizes all line orientations so that you don't have to specially handle edge cases. pajout has given the algebraic statement of the reasoning Re^2: Check if line is straight, which is good enough to answer what (we think) is the question, but it's good to keep the vector approach in mind.

As an erstwhile scientific programmer I still feel the need to point out that with floating point comparisons it might be a good idea to use a tolerance calculation somewhere....

In reply to Re^2: Check if line is straight by jaredor
in thread Check if line is straight by Anonymous Monk

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