Loops

Loops allow a program to repeat actions. Instead of writing the same code multiple times, a loop executes a block of code repeatedly while a condition holds or for a fixed number of iterations. Lua provides several loop constructs, each suited to different situations.

The while Loop

A while loop repeats as long as a condition evaluates to true.

while condition do
    -- repeated code
end

Example:

local count = 1

while count <= 5 do
    print(count)
    count = count + 1
end

The condition is checked before each iteration. If it is false initially, the loop body is never executed.

Avoiding Infinite Loops

If the condition never becomes false, the loop will run forever. This is called an infinite loop.

-- infinite loop
while true do
    print("Running...")
end

To avoid infinite loops, ensure that something inside the loop changes the condition.

The repeat ... until Loop

The repeat ... until loop executes the block at least once, because the condition is checked at the end.

repeat
    -- repeated code
until condition

Example:

local count = 1

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

The Numeric for Loop

The numeric for loop is used when the number of iterations is known in advance.

for variable = start, finish, step do
    -- repeated code
end

Example:

for i = 1, 5 do
    print(i)
end

The optional step value controls how much the variable changes each iteration:

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

The loop variable is local to the loop.

Looping Over Tables

Tables are commonly iterated using pairs or ipairs. ipairs is used for sequential numeric indices starting at 1:

local fruits = { "apple", "banana", "cherry" }

for i, value in ipairs(fruits) do
    print(i, value)
end

pairs iterates over all key–value pairs:

local scores = { alice = 10, bob = 15 }

for name, score in pairs(scores) do
    print(name, score)
end

The order of iteration with pairs is not guaranteed.

Breaking Out of Loops

The break statement stops a loop immediately.

for i = 1, 10 do
    if i == 5 then
        break
    end
    print(i)
end

After break, execution continues after the loop.

Skipping an Iteration

Lua does not have a built-in continue statement. Instead, conditional logic is used.

Example:

for i = 1, 5 do
    if i ~= 3 then
        print(i)
    end
end

another option, which I personally do not like, is to use goto command to jump to a label.

for i = 1, 10 do
  if i == 5 then
    goto continue
  end

  print(i)

  ::continue::
end

Nested Loops

Loops can be placed inside other loops.

for x = 1, 3 do
    for y = 1, 2 do
        print(x, y)
    end
end

Nested loops increase complexity and should be used carefully.

Common Loop Mistakes

Forgetting to update the loop variable:

-- infinite loop
while x < 10 do
    print(x)
end

Summary

Loops allow code to run repeatedly. Lua provides while, repeat ... until, and for loops for different situations. Numeric for loops are ideal when the iteration count is known, while while and repeat loops are better for condition-based repetition. Understanding how to safely exit loops and iterate over tables is essential for writing efficient programs.