Lua Variables & Data Types

Learn about variables, data types, and basic operations in Lua

Variables in Lua

Variables in Lua are used to store data values. Unlike many programming languages, Lua variables don't have types - only values do. This makes Lua very flexible.

variables.lua

-- Variable declaration and assignment
local name = "John"
local age = 25
local isActive = true

-- Printing variables
print(name)
print(age)

Local vs Global Variables

In Lua, variables can be either local or global. It's generally recommended to use local variables whenever possible for better performance and to avoid naming conflicts.

variable_scope.lua

-- Global variable (not recommended)
playerName = "GlobalPlayer"

-- Local variable (preferred)
local enemyName = "LocalEnemy"

function testScope()
  -- Can access global variables
  print(playerName)
  
  -- Can access local variables declared in the same scope
  print(enemyName)
  
  -- Local to the function
  local functionLocal = "I only exist in this function"
  print(functionLocal)
end

testScope()

-- This would error: print(functionLocal)

Data Types in Lua

Lua has eight basic types: nil, boolean, number, string, function, userdata, thread, and table.

Numbers

local integer = 42
local decimal = 3.14
local scientific = 1.25e6  -- 1,250,000
local hex = 0xFF  -- 255 in decimal

Numbers in Lua are double precision floating point by default. There's no separate integer type.

Strings

local single = 'Single quotes'
local double = "Double quotes"
local multiline = [[
  This is a
  multiline string
]]
local concat = "Hello " .. "World"  -- Concatenation

Strings are immutable sequences of characters. Use .. to concatenate strings.

Booleans

local isTrue = true
local isFalse = false

-- In conditionals, only false and nil are considered "falsy"
-- Everything else is "truthy" including 0 and empty strings
if isTrue then
  print("This will execute")
end

Boolean values represent true or false. In Lua, only false and nil are considered falsy.

Tables

-- Array-like table
local colors = {"red", "green", "blue"}

-- Dictionary-like table
local person = {
  name = "John",
  age = 30,
  isAdmin = true
}

-- Accessing values
print(colors[1])  -- "red" (Lua arrays are 1-indexed)
print(person.name)  -- "John"

Tables are the only data structure in Lua and can implement arrays, dictionaries, sets, and more.

type_checking.lua

-- Checking types with type() function
local name = "Lua"
local age = 30
local scores = {95, 87, 92}
local isValid = true

print(type(name))    -- "string"
print(type(age))     -- "number"
print(type(scores))  -- "table"
print(type(isValid)) -- "boolean"
print(type(print))   -- "function"
print(type(nil))     -- "nil"

Operators in Lua

Lua supports a variety of operators for arithmetic, comparison, logical operations, and more.

Arithmetic Operators

local a = 10
local b = 3

print(a + b)  -- Addition: 13
print(a - b)  -- Subtraction: 7
print(a * b)  -- Multiplication: 30
print(a / b)  -- Division: 3.3333...
print(a % b)  -- Modulo: 1
print(a ^ b)  -- Exponentiation: 1000

Comparison Operators

local a = 10
local b = 3

print(a == b)  -- Equal to: false
print(a ~= b)  -- Not equal to: true
print(a > b)   -- Greater than: true
print(a < b)   -- Less than: false
print(a >= b)  -- Greater than or equal to: true
print(a <= b)  -- Less than or equal to: false

Logical Operators

local a = true
local b = false

print(a and b)  -- Logical AND: false
print(a or b)   -- Logical OR: true
print(not a)    -- Logical NOT: false

-- Short-circuit evaluation
local x = nil
local y = x or "default"  -- y will be "default"

Concatenation & Length

local str1 = "Hello"
local str2 = "World"

print(str1 .. " " .. str2)  -- Concatenation: "Hello World"

local list = {10, 20, 30, 40}
print(#list)  -- Length: 4
print(#str1)  -- Length: 5

Coding Challenges

Test your understanding of Lua variables and data types with these interactive challenges.

Challenge 1: Variable Declaration & Types

Create three variables: a string named 'greeting' with value 'Hello, Lua!', a number named 'score' with value 95, and a boolean named 'isCompleted' with value true. Then print each variable.

editor.lua

Challenge 2: Working with Tables

Create a table named 'person' with keys 'name', 'age', and 'hobbies'. The 'hobbies' key should contain an array of at least two string values. Then print the person's name and their first hobby.

editor.lua

Challenge 3: Type Conversion

Convert the string '42' to a number, add 8 to it, and store the result in a variable called 'result'. Then convert that number back to a string and concatenate it with the text ' is the answer'.

editor.lua

Type Coercion in Lua

Lua will automatically convert between strings and numbers when needed:

type_coercion.lua

-- String to number conversion
local numberString = "42"
local number = tonumber(numberString)
print(number + 8)  -- 50

-- Number to string conversion
local num = 42
local str = tostring(num)
print(str .. " is the answer")  -- "42 is the answer"

-- Automatic conversion in arithmetic operations
print("5" + 2)  -- 7 (string "5" converted to number)

-- This would fail: print("hello" + 5)

Operations

Lua supports various arithmetic, comparison, and logical operations.

Arithmetic Operators

local a = 10
local b = 3

print(a + b)  -- Addition: 13
print(a - b)  -- Subtraction: 7
print(a * b)  -- Multiplication: 30
print(a / b)  -- Division: 3.3333...
print(a % b)  -- Modulo: 1
print(a ^ b)  -- Exponentiation: 1000

Comparison Operators

-- Equality: == (equal to) and ~= (not equal to)
print(5 == 5)   -- true
print(5 ~= 5)   -- false

-- Comparison operators
print(5 > 3)    -- true
print(5 < 3)    -- false
print(5 >= 5)   -- true
print(5 <= 3)   -- false

Logical Operators

-- and, or, not
print(true and false)  -- false
print(true or false)   -- true
print(not true)        -- false

-- Short-circuit evaluation
local x = nil
local y = x or "default"  -- y will be "default"

Next Lesson: Functions