Programming Basics

This will not be a full introduction to programming, but it will hit on a few particularly important items. Even if you don't know much about programming, you'll be able to follow along if you just understand these few things. If know programming already, you can skip all this stuff.

Variables

Variables are ways to store information with an easy-to-remember name. As the name "variable" implies, the information stored in the variable can vary, or change. In PICO-8, variables can hold numbers, text, and the value true or false. Here are a few examples of variables:

Some words are reserved and you can't use them for variable names (like the word function). You also can't start the name of a variable with a number.

Functions

Functions are a list of instructions for the computer that are all grouped together under one name. Functions are usually created if you have a certain set of actions you want the computer to do many different times.

Functions are written with parentheses after the name of the function. This is so you can give the function extra information in case it needs that extra information to do its job. Even if no extra information is needed, you still need to write the parentheses.

Here's an example function called draw_target(). It draws a target shape using filled circles. Note that it needs an X and a Y coordinate to do its job:

Maybe you noticed something: circfill() is a function too! It's a function built into PICO-8, so you don't have to write the steps yourself, but it's still a function. You give it an X/Y coordinate, a radius, and a color, and it draws a filled circle at X/Y, at that radius, and with that color. And circlfill() is just one of many built-in functions!

Usually a function just does the job you need it to do and that's that, like the draw_target() function above, or circlfill(). But sometimes you need a function to give back, or return, information when it's done doing all of its steps.

Say you make a function that does a bunch of math, but you want to know the result when it's done. In other words, you want it to return the result back to you. Easy enough. You just use return and then specify what you want it to return.

Here's a real example:

When that function gets run, the number returned would be 40. Since 40 is indeed greater than 25, the print() function would then happen.

Functions are the backbone of anything you will create in PICO-8. Most games are really just many, many functions strung together, each one making changes to things in the game as the players play. Really understanding how your code moves from one function to another is the key to being able to make great games.

Tables

Tables are a way to store a lot of information all together under one variable name. Most PICO-8 games will use a table at some point or another, so it's good to understand how they work.

When you add a piece of information, or value, to a table, it gets paired with a name or a number called a key. The key is what you use to get the information back out of the table. You can say, "Look up the information stored in that table using this key." Keys are like the index in a book.

If you add values to a table without setting the key, the key will automatically be assigned as a number. Let's see an example of what this looks like.

Now let's see how that looks in code. Take note how we create the player table using empty curly braces. Then we add the values with named keys.

For the items table, we create the table with the values inside the curly braces, but without names. The keys get automatically assigned as numbers.

That's how to get values into a table. But what about getting values back out? For keys that are names, you can just use table.key, such as player.x or player.alive. But for keys that are numbers, you use square brackets with the number of the key inside, such as items[1] or items[3].

If your table uses numbers for keys, you can find out how many values are stored in a table by using the number sign (#), such as #items. In our example, this would give you 3. This is useful if you have to loop through all the values in a table and do something with each value. Here's an example:

This starts i at 1 and counts to #items (which is 3). Each time, it will print the value at items[i]. Since i goes from 1 to 3, every item will be printed.