Chapter 2 - Variables

With programming we can do arithmetics.

What is 3 + 4?

It's 7!

Okay well let's test that. We can use print to make the number appear in our output console.

print(3 + 4)
--Output: 7

Run your code (meaning press F6 and then close the window to show the output) and your console should say 7.

Cool! Now what is a + b?

Uhm...

Well it could be anything. That's because "a" and "b" don't have a value. Let's change that.

a = 5
b = 3

Let's take another look, what is a + b? What we're really asking is "What is the value of a + the value of b?". In other words, what is 5 + 3? Which is 8.

To prove that a + b = 8, we're going to print it.

a = 5
b = 3
print(a + b)
--Output: 8

Run your code again.

Here a and b are what we call variables. A variable is a word in which you can store a value. The number 3 is always 3, and 7 is always 7, but a variable can be anything you want it to be. Hence the name variable.

The word in which you store a value can be almost anything.

sheep = 3
test = 20
PANTS = 1040
asdfghjkl = 42

Variables are case-sensitive. That means that when you have the same word, but with different casing, it's not treated as the same. For example

sheep = 3
SHEEP = 10
sHeEp = 200

are three different variables, with each their own value.

You can do more than just summing up numbers.

a = 20 - 10 --Subtraction
b = 20 * 10 --Multiplication
c = 20 / 10 --Division
d = 20 ^ 10 --Exponentiation

For numbers with decimals we use a dot.

a = 10.4
b = 2.63
c = 0.1
pi = 3.141592

Take a look at the following code:

X = 5
Y = 3
Z = X + Y

First we say X = 5. When we give a variable a value, we call that an assignment. We assign 5 to X, and 3 to Y. Next we assign X + Y to Z. So now Z equals 8. Remember that you can always check the value of a variable with print. If we were to change the value of X or Y after Z = X + Y, it would not affect Z. It would still be 8.

X = 5
Y = 3
Z = X + Y
X = 2
Y = 40
print(Z)
--Output: 8

This is because to the computer Z is not X + Y, it's simply 8.

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Strings

A variable can also store text.

text = "Hello World!"

This is what we call a string. Because it's a string of characters.

We can connect strings by using two dots (..)

name = "Daniel"
age = "25"
text = "Hello, my name is " .. name .. ", and I'm " .. age .. " years old."
print(text)
--Output: "Hello, my name is Daniel, and I'm 25 years old."

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Variable naming rules

There are a few rules when naming a variable. First of all, your variable may have a number in it, but not at the start.

test8 --Good
te8st --Good
8test --Bad, error!

Your variable name also can't include any special characters like @#$%^&*.

And finally, your variable name can't be a keyword. A keyword is a word that the programming language uses. Here's a list of keywords:

and       break     do        else      elseif
end       false     for       function  if
in        local     nil       not       or
repeat    return    then      true      until     while

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Usage

Variables can be used to keep track of things. For example, we can have the variable coins, and every time we pick up a coin we can do coins = coins + 1.

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Summary

Variables are words in which we can store a value like a number or text. You can name them whatever you want, with a few exceptions. Variables are case-sensitive.