Loops and Iteration in Lua

What Is a Loop?

A loop is a programming structure that repeats a block of code while a condition remains true or for a specific number of times.

In human terms:

• • Do something again
• • And again
• • Until a rule says stop

Real-Life Examples

• • Counting from 1 to 10
• • Reading every line in a file
• • Checking player health every frame in a game
• • Processing each item in a list

All of these require iteration.

Why Loops Are Essential

Without loops:

• • You would repeat code manually
• • Programs would be longer and error-prone
• • Automation would be nearly impossible

Example Without a Loop

print(1)
print(2)
print(3)
print(4)
print(5)

Example With a Loop

local i = 1
while i <= 5 do
    print(i)
    i = i + 1
end

Loops make programs scalable and maintainable.

Types of Loops in Lua

Lua provides four main looping constructs:

This part focuses on the while loop, as it teaches the core looping concept used everywhere.

Understanding Iteration

Iteration means:

• • Start at an initial state
• • Perform an action
• • Move toward a stopping condition

Every loop has three critical components:

1. Initialization
2. Condition
3. Update

The while Loop

The while loop repeats a block of code as long as a condition is true.

Syntax

while condition do
    -- code block
end

Basic Example

local count = 1

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

This loop:

• • Starts at 1
• • Stops after 5
• • Updates the counter every iteration

Infinite Loops

An infinite loop occurs when the condition never becomes false.

Example (Incorrect)

local i = 1

while i <= 5 do
    print(i)
end

This loop never updates i.

Why Infinite Loops Are Dangerous

• Program freezes
• CPU usage spikes
• Game engines lock up

Corrected Example

local i = 1

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

Using break in a while Loop

The break statement exits a loop immediately.

local i = 1

while true do
    print(i)
    if i == 5 then
        break
    end
    i = i + 1
end

This creates a controlled infinite loop.

What Is a repeat ... until Loop?

A repeat ... until loop executes its code at least once, and then checks a condition after the loop body runs.

This makes it fundamentally different from a while loop, which checks the condition before executing.

Syntax of repeat ... until

repeat
    -- code block
until condition

Important rules:

• • The loop body always runs at least once
• • The loop stops when the condition becomes true
• • The condition is evaluated at the end

Basic Example

local count = 1

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

Output:

1
2
3
4
5

Even if count started at 10, the loop would still run once.

The Numeric for Loop

Used when you know the exact range of values to iterate over.

Syntax:

for variable = start, stop, step do
    -- code
end

Standard Increment:

for i = 1, 10, 2 do
    print(i) -- Outputs: 1, 3, 5, 7, 9
end

Reverse Iteration:

for i = 10, 1, -1 do
    print(i) -- Counts down from 10 to 1
end

The Generic for Loop

Designed to traverse data structures using iterator functions.

Using ipairs (Arrays):

local fruits = {"Apple", "Banana", "Cherry"}

for index, value in ipairs(fruits) do
    print("Item " .. index .. " is " .. value)
end

Using pairs (Dictionaries):

local player = {name = "Hero", level = 50, class = "Warrior"}

for key, val in pairs(player) do
    print(key .. ": " .. val)
end

Loop Control: break and the continue Problem

The break Statement

Immediately terminates the innermost loop.

for i = 1, 100 do
    if i == 5 then break end
    print(i)
end
-- Output stops at 4

The Missing continue

Lua doesn't have continue. Use these patterns instead:

Method A: Using if (Recommended)

for i = 1, 10 do
    if i % 2 == 0 then
        print("Even number: " .. i)
    end
end

Method B: Using goto (Lua 5.2+)

for i = 1, 10 do
    if i % 2 == 0 then goto continue end
    print(i)
    ::continue::
end

Common Beginner Mistakes

• Forgetting to update the loop variable
• Using the wrong condition
• Overusing nested loops
• Not understanding loop exit flow