Lua basics in simple words: writing the first algorithms

Lua is a simple and powerful programming language that is great for beginners. Today we will analyze the three pillars of algorithms: conditions, loops, and functions. No complicated words, just practice!

Conditions: teaching the program to make decisions

Imagine that you are saying to a friend: "If it's raining outside, take an umbrella." You need to explain it to the computer in the same way!

Simple if condition

local погода = "Rain"

if погода == "Rain" then
    print("Let's take an umbrella!")
end

The program checks: if the weather is "rain", then it displays a message.

Condition with if-else alternative

local возраст = 16

if возраст >= 18 then
    print("You can drive a car")
else
    print("It's too early, you need to grow up")
end

If the age is greater than or equal to 18, the program will display one message, otherwise — another.

Several elseif options

local баллы = 85

if баллы >= 90 then
    print("Rating: excellent!")
elseif баллы >= 70 then
    print("Grade: good")
elseif баллы >= 50 then
    print("Grade: satisfactory")
else
    print("You need to improve your knowledge")
end

The program checks the conditions in order and executes the first suitable one.

Cycles: repeating actions

Why write the same code 100 times if you can tell the program: "Repeat this 100 times"?

While loop — while the condition is true

local счётчик = 1

while счётчик <= 5 do
    print("Repeat number " .. счётчик)
    счётчик = счётчик + 1
end

The program will repeat the action until the counter is greater than 5. Result:

Repetition number 1
Repetition number 2
Repetition number 3
Repetition number 4
Repeat number 5

The for loop — when we know how many times to repeat

-- От 1 до 10
for i = 1, 10 do
    print("Number: " .. i)
end

-- От 10 до 1 с шагом -1
for i = 10, 1, -1 do
    print("Countdown: " .. i)
end

This is the most convenient cycle when we know exactly the number of repetitions.

Repeat-until loop — at least once will be executed

local число = 0

repeat
    print("Number: " .. число)
    число = число + 1
until число > 3

The difference from while: this loop first performs the action, and then checks the condition.

Practical example: multiplication table

local число = 7

print("Multiplication table " .. число)
for i = 1, 10 do
    print(число .. " × " .. i .. " = " .. число * i)
end

Result:

7 × 1 = 7
7 × 2 = 14
7 × 3 = 21
...and so on

Functions: creating our own commands

A function is like a recipe. We write it down once, and we use it many times.

Simple function

function поздороваться()
    print("Hello, world!")
end

-- Вызываем функцию
поздороваться()

Function with parameters

function поздороваться_с_именем(имя)
    print("Hi, " .. имя .. "!")
end

поздороваться_с_именем("Alexey")
поздороваться_с_именем("Maria")

Result:

Hi Alexey!
Hi Maria!

Function with return value

function сложить(a, b)
    return a + b
end

local результат = сложить(5, 3)
print("5 + 3 = " .. результат)  -- Выведет: 5 + 3 = 8

Practical example: parity check

function чётное_или_нечётное(число)
    if число % 2 == 0 then
        return "even"
    else
        return "odd"
    end
end

print("10 is " .. чётное_или_нечётное(10))
print("7 is " .. чётное_или_нечётное(7))

Let's combine everything together

The real power of programming is when we combine conditions, loops, and functions!

-- Функция проверяет, простое ли число
function простое_число(n)
    if n < 2 then
        return false
    end
    
    for i = 2, n - 1 do
        if n % i == 0 then
            return false
        end
    end
    
    return true
end

-- Найдём все простые числа от 1 до 20
print("Prime numbers from 1 to 20:")
for число = 1, 20 do
    if простое_число(число) then
        print(число)
    end
end

This program will display: 2, 3, 5, 7, 11, 13, 17, 19

Useful tips for beginners

1. Indent — the code is easier to read:

-- Плохо
if x > 0 then
print("Positive")
end

-- Хорошо
if x > 0 then
    print("Positive")
end

2. Name the variables clearly:

-- Непонятно
local a = 25

-- Понятно
local возраст_пользователя = 25

3. Comment on the code:

-- Вычисляем площадь круга
local радиус = 5
local площадь = 3.14 * радиус * радиус

4. Start with the simple — first write the code without functions, then move the repeating parts into functions.

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