Types — numbers, strings, and booleans

A variable is a box. This lesson is about what can go in the box — because Luau won't let you mix everything together. Learn the four types now and you'll dodge a huge share of beginner errors later.

#The four types you'll use

Number — whole numbers, decimals, negatives. Health, speed, and time are all numbers.

local coins = 5
local speed = 3.5

String — text wrapped in quotes. "Sam" is a string; Sam without quotes is an error (Luau thinks you mean a variable named Sam).

local playerName = "Sam"

Boolean — only two values: true or false. Booleans are how your game says yes or no: "is the door open?", "did they win?"

local hasKey = false

nil — means "no value." A variable that has never been assigned holds nil.

#Why "1" is not 1

This is the trap that catches everyone:

print(1 + 1)    --> 2    (two numbers)
print("1" + 1)  --> ERROR: attempt to perform arithmetic on a string

The number 1 and the string "1" are completely different things. You can add numbers. You cannot add text.

Same for concatenation the other way — you can't glue a number onto a string without converting:

local coins = 5
print("You have " .. coins .. " coins.")  --> You have 5 coins.

Wait — that worked! When you glue with .., Luau is friendly and converts numbers to text for you. But when you try to add with +, it's strict. Memorize it: gluing is friendly, adding is strict.

#Converting on purpose

Sometimes you have a string that's actually a number — like the text from a UI input box, where the player typed "10". You need to convert it before math:

local typed = "10"
local amount = tonumber(typed)  -- "10" becomes 10

print(amount + 5)  --> 15

And the reverse — tostring turns anything into text when you need a string specifically:

local lives = 3
local text = tostring(lives)  -- 3 becomes "3"

local typed = "7"
-- your line here

#Common mistakes

• Forgetting quotes around text. local name = Sam errors; local name = "Sam" works.
• Trying to add player input directly. Numbers typed into a TextBox arrive as strings. Run them through tonumber first.
• Expecting .. and + to behave the same. .. converts for you, + refuses. Keep them straight.

Next lesson: doing the same job more than once — functions.