Variables, Types, and Control Flow

Lua is dynamically typed, a variable's type is decided by whatever value it currently holds, and can change at runtime.

Basic types

local xp = 100          -- number (Lua has no separate int/float, just "number")
local name = "Ada"       -- string
local passed = true      -- boolean
local nothing = nil      -- absence of a value
local scores = {90, 85, 100} -- table (used for arrays, maps, and objects)

print(type(xp), type(name), type(passed), type(nothing), type(scores))

nil is Lua's "no value", it's what an undeclared variable holds, and it's the only value besides false that counts as falsy in a condition.

Control flow

local xp = 45

if xp >= 50 then
  print("Level up!")
elseif xp >= 25 then
  print("Halfway there.")
else
  print("Keep going.")
end

for i = 1, 5 do
  print("Lesson " .. i)
end

local count = 0
while count < 3 do
  print("count = " .. count)
  count = count + 1
end

• Every block (if, for, while, functions) is closed with the keyword end, there are no curly braces in Lua.
• for i = 1, 5 do ... end is a numeric for loop: start, stop, and an optional step (for i = 10, 1, -1 counts down).
• Only nil and false are falsy, everything else, including 0 and "", is truthy. This is a common gotcha for people coming from JavaScript or Python.