Numeric for Loop
Iterate over numeric ranges with the for i=start,limit,step syntax.
Numeric for Loop is a free Lua Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Lua Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Numeric for Syntax
Lua's numeric for loop has the form for var = start, limit, step do. The step defaults to 1 if omitted. The loop variable is local to the loop body and cannot be modified inside. The limit and step are evaluated once before the loop starts.
-- Count 1 to 5
for i = 1, 5 do
io.write(i .. " ")
end
print() -- 1 2 3 4 5
-- Count with step 2
for i = 1, 10, 2 do
io.write(i .. " ")
end
print() -- 1 3 5 7 9Countdown with Negative Step
Use a negative step to count downward. The loop continues as long as var >= limit (when step is negative). If the start is already less than the limit with a negative step, the loop body never executes.
for i = 10, 1, -1 do
io.write(i .. " ")
end
print()
-- 10 9 8 7 6 5 4 3 2 1
-- Step -2
for i = 10, 0, -2 do
io.write(i .. " ")
end
print()
-- 10 8 6 4 2 0Loop Variable is Local
The loop control variable (i) is automatically local. You cannot change its value inside the loop — Lua ignores assignments to the loop variable. To track iterations differently, use a separate local variable.
for i = 1, 5 do
-- i is read-only inside the loop
-- i = i + 10 -- this creates a new global i, not the loop var
print(i) -- always 1, 2, 3, 4, 5 as expected
end
-- i is nil here (it was local to the loop)
print(i) -- nil (or whatever global i was)Iterating Arrays
The most common use of the numeric for is iterating arrays by index. Use #arr as the limit. Unlike ipairs, this form lets you control step size and iterate in reverse, and it's slightly faster for dense arrays.
local fruits = {"apple", "banana", "cherry", "date"}
for i = 1, #fruits do
print(i, fruits[i])
end
-- 1 apple
-- 2 banana
-- 3 cherry
-- 4 dateSumming with for
Numeric for loops are ideal for accumulating over arrays. The pattern is always the same: initialize a result variable before the loop, update it inside, and use it after.
local values = {10, 20, 30, 40, 50}
local total = 0
for i = 1, #values do
total = total + values[i]
end
print("Total:", total) -- 150
print("Count:", #values) -- 5
print("Mean:", total / #values) -- 30Nested Numeric for
Nest two numeric for loops for 2D operations like matrix traversal, table of tables, or generating coordinate pairs. The outer loop rows, the inner loop columns — each iteration accesses one cell.
local rows, cols = 3, 4
for r = 1, rows do
for c = 1, cols do
io.write(string.format("%2d ", r * c))
end
print()
end
-- 1 2 3 4
-- 2 4 6 8
-- 3 6 9 12Float Steps
The step and limits can be floating-point numbers, though this can introduce precision errors. For exact iteration counts, stick to integers. If you must use floats, be aware that the loop count is computed as floor((limit - start) / step) + 1.
-- Float step
for x = 0.0, 1.0, 0.25 do
io.write(x .. " ")
end
print()
-- 0.0 0.25 0.5 0.75 1.0
-- Prefer integer math when possible
for i = 0, 4 do
local x = i * 0.25
io.write(x .. " ")
endBuilding a Result Table
A numeric for loop is the standard way to build a new table from existing data. Create an empty table, then use the loop to fill it by index.
local source = {1, 2, 3, 4, 5}
local squares = {}
for i = 1, #source do
squares[i] = source[i] ^ 2
end
for i = 1, #squares do
print(squares[i]) -- 1, 4, 9, 16, 25
endbreak in Numeric for
You can exit a numeric for early with break. Execution jumps to the statement after end. This is useful for linear search: iterate until the target is found, then break.
local data = {5, 3, 8, 1, 9, 2, 7}
local target = 9
local foundAt = nil
for i = 1, #data do
if data[i] == target then
foundAt = i
break
end
end
if foundAt then
print("Found at index " .. foundAt) -- 5
else
print("Not found")
endLoop Count Calculation
The number of iterations of for i = start, limit, step is max(0, floor((limit - start) / step) + 1). Understanding this prevents off-by-one errors. When step is 1, the count is simply limit - start + 1.
-- How many iterations?
local count = 0
for i = 1, 10, 3 do
count = count + 1
end
print(count) -- 4 (i = 1, 4, 7, 10)
count = 0
for i = 5, 1 do -- step=1 but start > limit
count = count + 1
end
print(count) -- 0 (no iterations)Quick Check
What does for i = 10, 1, -3 do iterate over?
Recap: Numeric for
Summary:
for i = start, limit, step do— step defaults to 1- Negative step for countdown
- Loop variable is automatically local and read-only
- Limit and step evaluated once before loop starts
breakexits early- Standard pattern: build result tables, search arrays, accumulate sums
Frequently asked questions
Is the “Numeric for Loop” lesson free?
Yes — the full text of “Numeric for Loop” is free to read here on the web, and the Lua Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Lua Academy course, upgrade to CoddyKit PRO.
What will I learn in “Numeric for Loop”?
Iterate over numeric ranges with the for i=start,limit,step syntax. You practise Lua Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Lua Academy?
No prior experience is required. Lua Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Numeric for Loop” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Lua Academy lesson?
Yes. Every Lua Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.