Lua Control Statements

Learn conditional branches and loops, the essential control statements used to build Lua programs.
Tags:

Conditional Branches with if and else

Use if, elseif, and else to select a branch.

if condition then
  statements
elseif another_condition then
  statements
else
  statements
end

score = 70
if score >= 60 then
  print("Pass")
else
  print("Fail")
end

Use == for equality and ~= for inequality.

In Lua, only false and nil are false conditions. Unlike C, the number 0 is true.

Relational Operators

Operator Meaning
x < y x is less than y
x > y x is greater than y
x <= y x is less than or equal to y
x >= y x is greater than or equal to y
x == y x equals y
x ~= y x does not equal y

Loops

Use while to repeat while a condition is true.

i = 1
while i <= 10 do
  print(i .. ": Hello world!")
  i = i + 1
end

Use numeric for when the range is known.

for i = 1, 10 do
  print(i .. ": Hello world!")
end

Specify a step as the third value.

for i = 1, 10, 4 do
  print(i)
end

Use repeat when the loop body must run at least once. The loop ends when the until condition becomes true.

i = 1
repeat
  print(i)
  i = i + 1
until i >= 5

Use break to exit a loop early.

for i = 0, 10 do
  print(i)
  if i == 5 then break end
end

Lua does not provide built-in switch or continue statements.

Example: Multiplication Table

for i = 1, 9 do
  for j = 1, 9 do
    io.write(string.format("%3d", i * j))
  end
  io.write("\n")
end

io.write() does not add an automatic newline. The %3d format reserves three character positions.