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Ask Slashdot: What's the Harm In a Default Setting For Div By Zero?
New submitter CodeInspired writes: After 20 years of programming, I've decided I'm tired of checking for div by zero. Would there be any serious harm in allowing a system wide setting that said div by zero simply equals zero? Maybe it exists already, not sure. But I run into it all the time in every language I've worked with. Does anyone want their div by zero errors to result in anything other than zero?
Does anyone want their div by zero errors to result in anything other than zero?
Yes.
It means your code is wrong. Who knows what led up to that /0 error.
"Rather than failing when an unexpected condition arises, I want all software on my system to continue running with a possibly invalid or meaningless internal state."
Sure, what could go wrong?
So how do you know if you had an error if you return "0" for a divide by 0 error? Now you have a whole 'nother set of problems to code around.
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Because that usually means I'm trying to do something that's mathematically meaningless and I'd rather handle the special case than silently get a meaningless result.
I think infinity makes a bit more sense than zero. And max is the closest thing to infinity.
You want to find out how many Euros in those Zimbabwean dollars you're keeping track of. The exchange rate fluctuates. The web-API you're using goes offline and returns zero, so you divide by zero. Whoops. How do you tell the difference between worthless numbers and just worthless currency?
You want to draw an interlaced gif of some sort, so you do every nth line, then every n-1th line, as you get the interlaced lines and work down towards a full image with every row drawn. And then you cock up at the end, accidentally hit zero and you overwrite the first line thousands of times with garbage rather than spot the mistake.
Zero is so completely the wrong answer, you don't even understand why. The actual real answer shouldn't even be the largest integer you can hold. And if it is, it could also be the smallest (i.e. largest negative). But actually it's none of them.
Division by zero is NOT something that produces a number. It cannot happen. It cannot return zero (which is incredibly wrong), nor can it return any single other consistent constant. It should actually just error, which is why it does. It should produce something that's not a number (NaN). And it does exactly that.
Divide by zero is like a null pointer. On the face of it is appears singularly useless. Why on earth would you want a pointer that you can't dereference? But it's there as an indicator. You cocked up. Majorly. If your maths is at all important at that point (a cell in a spreadsheet), then you're potentially losing billions of digits of accuracy.
You can continue on blindly with your cockup quite easily. Any idiot can overload the divide operator to return zero when the denominator is zero. And you won't get any of those nasty errors. Errors which are indicative of an earlier error that you're just ignoring.
There's a reason that, even back in the days of BASIC and very limited ROM space, you programmed in divide by zero as an error rather than just returning zero and documenting it. It's the same reason that you don't just "ignore" NULL pointer dereferences by saying "Oh, well, we won't call that function and just carry on from where we were then". Any idiot could make some kind of overload to allow that as well if they really wanted.
The fact is that if you're dividing by zero you're doing something that's mathematically impossible. There is no amount of zeroes you can multiply to get anything other than zero. Not even if you multiply infinities of zeroes do you get anything other than zero. Hence division by zero of any non-zero integer is IMPOSSIBLE. It doesn't have an answer.
And, like the square root of -1, if you just ignore it and pretend it exists you will run into all kinds of trouble. If you want to do something with it, in the same way that we use "i" to represent the square root of -1 to get lots of magical maths that actually works, use a language that recognises NaN and test against it.
But I'll tell you now that it's quicker and easier to test if you're dividing by zero BEFORE you do the divide.
Dividing any other number than zero by zero is well defined as infinity or minus infinity.
We need a -1 Wrong mod for just this sort of post.
You think *you're* having problems. I'm seeing actual stories with titles like "Ask Slashdot: What's the Harm In a Default Setting For Div By Zero?"