Why is divide by zero a problem?

Question

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UPDATE: Christ! I had another look at the program, to see if I was being silly. And indeed I am. The error was in fact not a divide by zero error but 'ArrayIndexOutOfBoundsException:0' This is because because damageTaken is actually an array of values that stores many different 'damages'. So the equation I have is probably correct, and the problem I have now is entirely different from the initial title or question.

I'm giving the point to Thomas O for providing the apples analogy that perfectly answers the question of why.

Thank you so much for your input.

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Rest assured I have searched for an answer before asking this question:

In java I'm trying to create a progress bar. Our example: damage incurred, in a racing game, by setting the value for height as a percentage of maxmimum damage allowed before gameover.

At the start of the program damageTaken = 0;

(damageTaken / maximumDamage)

will give numbers between 0 - 1.

Then I just multiply that by the height of the progress bar, to create a fill bar of the appropriate height.

But of course, when damageTaken = 0 we are dividing by zero!!! So program crashes. And I want the progress bar to be of zero height!

why can't It just spit out 0 as the sum? And how do I get around this?

Answer 1

(damageTaken / maximumDamage)

is dividing by zero ONLY if maximumDamage is zero.

If damageTaken is zero, there is no problem.

Answer 2

Just add a special case for 0;

private int getProgress()
    if (damageTaken == 0) {
        return 0;
    } else {
        return (damageTaken / maximumDamage) * progress.getHeight();
    }
}

However, (and it's a big however) the reason you are getting divide by 0 is because maximumDamage is 0, not damageTaken. So, what you probably really want is:

private int getProgress()
    if (maximumDamage== 0) {
        return 0;
    } else {
        return (damageTaken / maximumDamage) * progress.getHeight();
    }
}

Answer 3

You are not dividing by zero, you are dividing zero by something.

It is completely allowed to take two halves of zero. The answer is zero. Say you have zero apples. You split your zero apples between Alice and Bob. Alice and Bob now both have zero apples.

But, you cannot divide by zero. Say you have two apples. Now, you want to give these apples to zero people. How many apples does each person get? The answer is undefined, and so division by zero is impossible.

Answer 4

[ignore me, sorry]

Answer 5

Let's stop talking about illegality, as though uniformed mathematics police were about to storm the room. ;) For the mathematical reasoning behind this, this related question is useful.

It is fair to ask why, after all this time, modern programming platforms don't handle division-by-zero errors for us in some standard way - but to answer the question: Java, like most any other platform, throws an error when division by zero occurs. In general, you can either:

• Handle before: check the variable to be used as your denominator for zero before doing the division
• Handle after: you can catch the exception thrown when the division by zero occurs and handle it gracefully.

Note that, as good practice, the second method is only appropriate when you wouldn't expect the variable to ever be zero under normal system operation.

So yes, you need a special case to handle this situation. Welcome to programming. ;)