The 3DGS Nerd

Modulo – The Mystery Operator

Well, most people – mainly beginners – are very confused about what this “%” or “Modulo” operator does. Well simply put, it returns the “remainder” of a division. Let’s take a look at some easy-to-understand examples:

Let’s do something simple:

4 / 2 = 2 – Rest: 0

We all know how to do this, 2 fits two times into 4, nothing remains and thus rest is = 0.
The modulo operation to get this “0” would be

var rest = 4 % 2;

Now let’s actually take it into account with something that gives us some “rest”:

5 / 2 = 2.5; Rest: 1

Okay, stop now. That doesn’t make sense. Right?! 2.5 times 2 is 5, there is nothing left over!? Well no. If you make a modulo operation, it is as if you make the division with integer numbers. In this case this means:

5 / 2 = 4; Rest 1

Because as an integer number, 2 only fits two times inside 5. And the remainder of the operation is 1, the number it takes to make the full 5.

And again, in modulo this is:

var rest = 5 % 2; // = 1

One more example before I go into “real-life-application” examples:

8 / 3 = 2.666~; Rest: 2 – Or in Modulo result:

8 / 3 = 2; Rest: 2

Okay, let’s make this a real life example. For instance, a simple function that tell us if the a number is odd or even:

function IsEven(num)

{

    return !(num % 2);

}

This is easy explained. The function calculates the modulo for the division “num/2” if the number is even, the result will be 0. As the function is called “IsEven” I invert the result (using !) so that instead of 0 it returns 1. If the function would be called “IsOdd” you can leave it without the !, like this:

function IsOdd(num)

{

    return (num % 2);

}

We can even use it in a clever way to execute something every n’th frame:

...

while(1)

{

    if(total_frames % 5 == 0) // every 5 frames

    {

        temp += 1; // add 1 to temp

    }

    wait(1);

}

...

Modulo is a great way to do counters and do lots of tricky operations in just a matter of a single line. If you know how to use it, modulo is a mighty operator and can optimize your code BIG TIME.

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