This is Part 3 in a series on learning how to program your own Arduboy game. If you have skipped the previous parts, please read over Part 1 and Part 2!
Variables
Computers work a lot with calculations and data. To make most video games, you’re going to need to be able to store data, like high scores, or player location, or lives remaining. In order to remember data, a computer must set aside some memory to put that data into. Then, the computer can be told to change the data stored there.
Loops
Remember how I said that computers have to be given specific instructions? Ever notice how the back of shampoo bottles say to 1. Lather , 2. Rinse , 3. Repeat ? If a computer were given those instructions, they would be stuck in an infinite loop of lathering, rinsing, and repeating. In programming, having instructions repeat in a loop can be very useful. I’ll show you how to use the loop() function to do this.
Getting Started
In this program, we’re going to make the Arduboy keep track of a number and display it to you as it is increased.
Let’s do it! Grab the code from the previous tutorial so that we can build off of it:
//Jonathan Holmes (crait)
//October 18th, 2016
//Printing Text
#include <Arduboy2.h>
Arduboy2 arduboy;
void setup() {
// put your setup code here, to run once:
arduboy.begin();
arduboy.clear();
arduboy.print("Holmes is cool!");
arduboy.display();
}
void loop() {
// put your main code here, to run repeatedly:
}
Initialization
Whenever you create a variable, you have to initialize it, which is setting aside memory for the data and giving it a name. You’ve already done this but didn’t realize it. Check out the Arduboy arduboy; line. You initialized an object called arduboy . Objects are a lil’ more complex than I want to get into during this tutorial, but there are different kinds of variables that you can initialize. Here are some: Integers, booleans, characters, objects, doubles, and many more.
We’ll initialize our number that’s going to increase as an integer. This basically means that it’s a whole number, without fractions. Integers will appear as int inside of C++ code.
To initialize a variable, you must put 3 things: The type of variable, the name of the variable, then a semi-colon. Let’s call our variable counter . Here’s the code: int counter; Put it under the Arduboy arduboy; line.
Assignment
Whenever you create a variable, you can give it a value. This is called assignment . We don’t know what counter 's value is because we never gave it one.
Let’s clean up the code by removing the arduboy.print(); and arduboy.display() functions from setup() . Instead, let’s put the assignment there:
counter = 0;
This line of code is saying that counter 's value is now equal to 0. Instead of 0, you could put another number, a mathematical formula, or some other things that I’ll explain below.
Here’s what your code should look like:
//Jonathan Holmes (crait)
//October 18th, 2016
//Counter
#include <Arduboy2.h>
Arduboy2 arduboy;
int counter;
void setup() {
// put your setup code here, to run once:
arduboy.begin();
arduboy.clear();
counter = 0;
}
void loop() {
// put your main code here, to run repeatedly:
}
Incrementing
Okay, our program will be repeating a few simple instructions over and over again. Basically, we’ll change the value of counter , then display the value of counter , then repeat. To do this, we should add some code into the loop() function.
counter = counter + 1;
This line of code means that you are assigning the value of counter to itself plus 1. Or, in other words, counter 's value is now equal to the value of counter + 1.
Displaying The Variable’s Value
Now that we have the variable increasing, let’s display it! Remember how we used arduboy.print() to print some text to the screen? Well, we can use that same function to display numbers to the screen, too. Add arduboy.print(counter); .
If you were to run this code as it is, now, then the Arduboy’s screen would fill up with numbers. If we’re going to print something new, we need to be sure to erase what was previously on the screen. We need to add in arduboy.clear(); at the beginning of loop() and arduboy.display(); at the end to display the updated screen.
Have you ever used a type writer? Whenever you type letters, the cursor moves over. The arduboy.print() function works similarly. Every time you use the arduboy.print() function, it moves the cursor over. So we need to reset the cursor to the top of the screen with arduboy.setCursor(0, 0); . I will explain this more in a later tutorial, but just throw that at the top of the loop() .
The Completed Code
I’ve added in some comments, but your code should look like the following:
//Jonathan Holmes (crait)
//October 18th, 2016
//Printing Text
//Include the Arduboy Library
#include <Arduboy2.h>
//Initialize the arduboy object
Arduboy2 arduboy;
//Initialize our counter variable
int counter;
//The setup() function runs once when you turn your Arduboy on
void setup() {
//Start the Arduboy properly and display the Arduboy logo
arduboy.begin();
//Get rid of the Arduboy logo and clear the screen
arduboy.clear();
//Assign our counter variable to be equal to 0
counter = 0;
}
//The loop() function repeats forever after setup() is done
void loop() {
//Clear whatever is printed on the screen
arduboy.clear();
//Move the cursor back to the top-left of the screen
arduboy.setCursor(0, 0);
//Increase counter's value by 1
counter = counter + 1;
//Print out the value of counter
arduboy.print(counter);
//Refresh the screen to show whatever's printed to it
arduboy.display();
}
Running The Code
Connect your Arduboy to your computer and upload this code to it. Your Arduboy should start counting up!
What’s Next?
In the next tutorial, we’ll be learning about testing the values of variables, booleans, and pressing buttons! Click here to go to Part 4!
Credits
I wrote this tutorial in order to give back to the programming community that taught me to get into it about 10 years ago. If you’d like to follow me on Twitter, please do so at http://www.twitter.com/crait . I’d greatly appreciate that. 
).