Control Flow

By the end of this lesson you'll be able to make decisions with if / elseif / else , compare and combine values with Lua's word-based operators, and repeat work with every kind of Lua loop — while side-stepping the truthiness trap that catches developers from every other language.

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Part of the free Lua course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

Think of control flow as the signs and roundabouts on a road trip. An if is a junction: "is the light red? then stop, else go." A loop is a roundabout you keep circling until a condition lets you exit — break is the exit ramp you take the moment you spot your turn. Your code, like a car, only ever drives ONE path at a time; the conditions decide which. Get the signs right and the journey runs itself; get one backwards and you loop forever.

1. Making Decisions with if / elseif / else

An if runs a block of code only when a condition is true . Add elseif branches to test more conditions, and a final else to catch everything left over. Lua checks the tests top to bottom and runs the first one that is true, then jumps to end . Two things to burn in now: the branch keyword is the single word elseif (not else if ), and every if must be closed with end . Read this worked example, then you'll write your own.

2. Relational Operators (and the ~= surprise)

Conditions are usually built from relational operators that compare two values and return true or false . Most are familiar: , , , , and == for "equal to". The one to memorise is "not equal" : in Lua it is ~= (tilde-equals), not != . Writing != is a syntax error, so pair them in your head: equal is == , not-equal is ~= .

3. Combining Conditions: and / or / not

To join conditions, Lua uses words , not symbols: and , or , and not (there is no && , || , or ! ). and needs both sides true; or needs at least one; not flips a value. Lua also has no ternary operator, so the community idiom cond and a or b stands in for "if cond then a else b" — handy for picking one of two values on a single line.

In Lua, the only falsy values are nil and false . Everything else is truthy — including the number 0 , the empty string "" , and an empty table {' '} . If you come from JavaScript, Python, or C, this is backwards from what you expect, where 0 and "" are falsy.

So to check for zero you must be explicit — write if count == 0 then , never rely on 0 being falsy.

The program below is almost complete — fill in the three blanks marked ___ using the hints in the comments, then run it and check your output matches.

4. Repeating Work with Loops

A loop runs a block of code over and over. Lua gives you three forms. The numeric for counts: for i = start, stop, step do (the step is optional and defaults to 1). The while loop repeats while a condition stays true, checking it at the top. The repeat...until loop runs the body first and tests at the bottom, so it always runs at least once. Note Lua has no ++ or -= , so you update counters in full like fuel = fuel - 1 .

5. Looping Over Tables: pairs & ipairs

The generic for walks over a table. Use ipairs(t) for list-style tables — it visits integer keys 1, 2, 3... in order and stops at the first gap. Use pairs(t) to visit every key, including string keys like "name" , though the order is not guaranteed. Exit any loop early with break . There is no continue in Lua — to skip an item, invert the test and wrap the rest of the body in an if .

Two small gaps here: complete the numeric for's stop value, then add the keyword that exits a loop the moment a match is found. Fill in the blanks and run it.

No blanks this time — just a brief and an outline to keep you on track. FizzBuzz combines a loop, modulo, and the full if / elseif / else ladder, so it's the perfect end-of-lesson test. Build it, run it, and check your output against the example in the comments.

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