% Modulo Function Explanation
Since I spent almost a day hunting for the mysterious "%" to find out what it means and how to use it, I thought I share this super helpful explanation by @firemaplegames with all the other noobies and math failures like me still scratching their heads.
I also found it helpful to try the examples with a calculator at hand http://calculator.sdsu.edu/calculator.php
because the first examples
10 % 3 = 1
and
(any number)%2 = odd or even
that was easy to understand but the 99 coins example still had me scratching my head.
Lightbulb flashing when I found out that e.g 70%99 = 70
Hope somebody else makes this as happy as it made me.
I really would love it if there was a section in the cookbook that had such helpful examples for every operator and function.
Or maybe there could be a section in this forum entirely for that? Just threads tend to be bit unorganized to find stuff when you need it. Any ideas how to make something like this happen?
Thank you Joe!!
I found it here: http://forums.gamesalad.com/discussion/1885/no-mod-funtion
the modulo operatator, %, is used to find the remainder after division.
so: 10 % 3 = 1
because 3 goes into the number 10 exactly 3 times, with 1 left over.
and 8 % 4 = 0
because 4 goes into the number 8 exactly 2 times, with 0 left over.
and 17 % 6 = 5
because 6 goes into the number 17 exactly 2 times, with 5 left over.
Well, that's all well and good you say, but how could I possibly benefit from that?!?
That seems like the most useless math function. I could not ever possibly imagine using it!
Ah! But the mod function is very powerful, and used all the time in computer programming:
Here are a few quick examples:
It is used to quickly tell if a number is even or odd. Like this:
(ANYNUMBER) % 2
This will return 0 for an even number, 1 for an odd number.
In GameSalad, it would look like this:
Change Attribute: game.evenOrOdd To: myNumberToTest % 2
When game.evenOrOdd = 0
Display Text: "This number is Even!"
Otherwise
Display Text: "This number is Odd!"
Using that same exact logic, programmers use it to create "zebra stripes" in html tables. I'm sure you've seen a table of data that has alternating white and light gray lines. Your iTunes music library, for example. (although it's very subtle) uses this.
That effect is created like this:
If myCurrentRow % 2 = 0
Use the light gray background
Otherwise
Use the white background
The same logic again for a "toggle" switch:
Make an integer attribute. game.Switch
When you press the mouse button, or touch(pressed) the actor:
Change Attribute: game.Switch = (game.Switch + 1)%2
So the value of Switch is either 0 or 1. You can check for those values.
Another very handy use of the modulo is to use if for setting a limit on something.
This is used a lot in games as well.
Let's say your character collects coins in the game. Like in Super Mario Bros.. Mario can collect 99 coins, then the counter resets to 0, and it keeps going like this forever.
Well the "coin limit" is 99.
And you can use the modulo like this:
So every time Mario gets a coin, do this:
game.totalCoins = game.totalCoins+1%99
Every time the coin counter hits the limit, in this case 99, the counter resets to 0
But it doesn't just have to be a number, it can be an actor's width, or its alpha. anything, really:
self.maxWidth = 250
self.size.width = self.size.width+10%self.maxWidth
Or how about this:
In Asteroids, I want to give the player a bonus ship every 20,000 points
You would do that like this:
If currentScore%20000 = 0
Award a bonus ship
This will happen at 20000,40000,60000 etc...
Or if you're mean:
I want Space Invaders to get harder for every 2 minutes that the Player is at the machine:
if currentTimePlayedinSeconds%120
AlienFireRate=AlienFireRate+1
Or for laying out a grid, or chessboard, in a puzzle game
(you would use this in a loop)
gridSquareX = (currentGridSquareNum%numColumns)*gridSquareWidth
currentGridSquareNum = currentGridSquareNum+1
That should give you some basic ideas!
Hope this helps!
Joe
I also found it helpful to try the examples with a calculator at hand http://calculator.sdsu.edu/calculator.php
because the first examples
10 % 3 = 1
and
(any number)%2 = odd or even
that was easy to understand but the 99 coins example still had me scratching my head.
Lightbulb flashing when I found out that e.g 70%99 = 70
Hope somebody else makes this as happy as it made me.
I really would love it if there was a section in the cookbook that had such helpful examples for every operator and function.
Or maybe there could be a section in this forum entirely for that? Just threads tend to be bit unorganized to find stuff when you need it. Any ideas how to make something like this happen?
Thank you Joe!!
Comments
Please use mod instead. '%' might get used for other things in other platforms, and since we can't totally phase it out since it could break your older projects, it is less prone to other issues if you use mod(x,y).
let's see if I can get it right:
Change Attribute: game.Switch = (game.Switch + 1)%2
would be:
game.Switch = mod((game.Switch + 1),2)
and
self.size.width = self.size.width+10%self.maxWidth
would be:
self.size.width = mod( self.size.width+10 , self.maxWidth )
Is that right?
And is it allowed to put some spaces where the comma is inside the brackets? get's so hard to see what's going on like this.
Also you can do this
game.Switch = mod(game.Switch+1,2)
with less parenthesis.
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