LUA Cheatsheet for starting to program in Lua for experienced developers

lua-cheatsheet.lua

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------------LUA SUMMARY-------------------------------------------
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--This is a comment. For Lua, comments are invisible.
--We can type everything we want in here, without causing errors
--To make a multi-line comment we use --[[]]


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----------VARIABLES--------------
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--This is a variable.
x = 100


--A variable can be named everything, except Lua's keywords.
--Here's the list of keywords:
--[[
 	and       break     do        else      elseif
    end       false     for       function  if
    in        local     nil       not       or
    repeat    return    then      true      until     while
]]
--Also no symbols like !#@%~^&
--You can use numbers, but not as first character

--When using multiple words, use camelcasing (style preference)
--After the first word, every new word starts with an uppercase
thisIsCalledCamelCasing = 100

--You can output the value of a variable with
print(x)

--You can get the type of a variable with
type(x)

--So to output the type of a variable you do
print(type(x))


--Type of variables:

--Number
exampleNumber = 123

--String
exampleString = "Hello"

--Boolean
exampleBoolean = true

--Function
exampleFunction = function () end

--Table
exampleTable = {}

--And nil (no value)
exampleNoValue = nil

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---NUMBER---
------------
exampleNumber = 100

--Use a . for decimals not a ,
exampleNumber = 123.456

--You can skip the zero for numbers lower than 1
exampleNumber = 0.456
exampleNumber = .456

exampleNumber = 10 + 10 -- Addition
exampleNumber = 30 - 10 -- Substraction
exampleNumber = 2 * 10  -- Multiplication
exampleNumber = 10 / 5  -- Division
exampleNumber = 5 ^ 2   -- Exponentiation
exampleNumber = 38 % 10 -- Modulation
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---STRINGS---
-------------
--How to make one
exampleString = "Hello"
--Single quotes is fine as well
exampleString = 'Hello'
-- Use [[]] for multiple line strings
exampleString = [[ Hello
how
are
you?]]

--Combine strings with ..
exampleString = "Hello " .. "World!"
--You can use numbers as well
exampleString = "I am " .. 4 .. "years old"
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---BOOLEAN---
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--There are only 2 booleans:
exampleBoolean = true
exampleBoolean = false

--A condition is also a boolean
exampleBoolean = 5 > 10 --True

--Conditions are made like this:
exampleBoolean = 5 > 10 --Higher than (false)
exampleBoolean = 7 < 7 --Lower than (false)
exampleBoolean = 7 >= 7 --Higher than or equal to (true)
exampleBoolean = 7 <= 3 --Lower than or equal to (false)
exampleBoolean = 7 == 4 --Equal to (false)
exampleBoolean = 7 ~= 4 --Not equal to (true)

-- == and ~= can also be used with any type of variable
exampleBoolean = "hello" == "world" --False 
exampleBoolean = true ~= false --True
exampleBoolean = {} == 14 --False

--False (Every new table is unique)
exampleBoolean = {1,2,3} == {1,2,3}

--False (Every new function is unique)
exampleBoolean = function() end == function() end

--You can use "and" to check if multiple conditions are true
exampleBoolean = 10 > 3 and 7 < 2 --False (Only one condition is true)
--You can use "or" to check if one of the conditions is true
exampleBoolean = 10 > 3 or 7 < 2 --True (One of the conditions is true)



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---FUNCTIONS---
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exampleFunction = function () end

--But normally typed like this:
function exampleFunction() end

--You call a function like this:
exampleFunction()

--A function can return a value
test = exampleFunction() -- test = returned value

--Without the (), it's the function itself 
test = exampleFunction --test = the function exampleFunction

--You can add parameters
function exampleFunction(hello, what, test)
	--hello, what and test here are what we call "parameters"
end

--We call the function with values
--The given values are what we call "arguments"
exampleFunction(10, "example", true)
--hello becomes 10
--what becomes "example"
--test becomes true
--But only in that function call

--In this function call, hello, what and test are nil again (no value)
exampleFunction()

--We can return a value with the "return" keyword

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

--You can use ...
--for if you're not sure how many parameters a function needs
function exampleTest(a, b, ...)
	print(a, b, ...)
end

exampleTest(1,2,3,4,5,6,70,80,900,1000)

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---TABLES----
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exampleTable = {}

--Adding values to a table
--When creating the table:
exampleTable = {123, "hello", true}

--With table.insert()
table.insert(exampleTable, 100)

--With []
exampleTable[5] = "world"
exampleTable["test"] = "what"

--But in the case of test you should use . (style preference)
--These are called keys
exampleTable.test = "what"

--You can add keys when creating the table like this:
exampleTable = {test = "what", thing = "hello"}

--You can add any type of variable
exampleTable = {function () return "really?" end}

--You can access the variable with []
print(exampleTable[1]()) --calls the function inside the table

--You can also add tables
exampleTable = {{"wat", "oke"}, {"ehm", "sorry"}}

print(exampleTable[2][1]) --"ehm" (the first value of the second table)

--Use # to get the length of a table
print(#exampleTable)

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------------FLOW CONTROL---------------
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---IF STATEMENTS----
--------------------
if exampleBoolean then
	--Everything inside here will only be executed when exampleBoolean (the condition)
	--is not false or nil
end

--Will the inside of the if-statement be executed?
if false then end --No
if nil then end --No
if true then end --Yes
if 5 > 10 then end --Yes
if 5 < 10 then end --No
if 123 then end --Yes
if "test" then end --Yes
if {1, 2, "hello"} then end --Yes
if function () end then end --Yes

--"else" will be executed when the condition fails
if 4 > 7 then
	--Will not be executed
else
	--Will be executed
end

--You can add multiple elseifs

if 5 > 10 then
	--Will not be executed
elseif 3 > 9 then
	--Will not be executed
elseif 6 > 2 then
	--Will be executed
elseif 10 > 4 then
	--Will not be executed, because above already got executed.
	--It's an else, meaning: if above condition fails then..
else
	--Will not be executed
end

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---LOOPS----
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for i=1,10 do
	print(i) --Prints the number 1 to 10
end

--i is a variable so can be named anything
--The first number is the start, the second number is the end
--The third number is the increase every loop 
for number=5,120,10 do
	print(number) --Prints 5, 15, 25, etc.
	if number == 45 then
		break --Use break to stop a for-loop
	end
end

for i=1,#exampleTable do
	print(exampleTable[i]) --Print all the values in a table
end

--But for that you should use this
for i,v in ipairs(exampleTable) do
	print(v) --v == exampleTable[i]
end

--Unless you want to loop through the keys
exampleTable = {test = "what", thing = 123}

--Then you use this
for k,v in pairs(exampleTable) do
	print(k) --k is the key, so "test", "thing"
	print(v) --v is the value, so "what" and 123
			 --exampleTable[k] == v
end

--This is a while loop
while exampleBoolean do
	if exampleNumber > 100 then
		exampleBoolean = false --exampleBoolean is now false and the loop stops
	else
		exampleNumber = exampleNumber + 1
	end
end

--It continues till the statement is false
--Be careful with these
--If your statement will always be true your program gets stuck.

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-----LOCAL VARIABLES------------------
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--Only available in this file
local exampleLocal = 100

function exampleFunction()
	local exampleLocal2 --Only available inside this function
	if true then
		--Only available in this if-statement
		local exampleLocal3 = 50
		for i=1,10 do
			--Only available inside this for-loop
			local exampleLocal4 = 20
		end
	end
end

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-----TERNARY OPERATORS----------------
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z = exampleBoolean and exampleNumber or exampleString

--Z = A and B or C
--if A is not false (or nil), then Z will become B, else Z becomes C
--This is called a ternary operator.

function exampleFunction(a, b)
	a = a or 0 --if a is false or nil, then it becomes 0
	b = b or 0 --if b is false or nil, then it becomes 0
	return a + b
end

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-----OTHER----------------------------
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--Spaces and enters (new lines) don't matter
test 
=
3
function exampleFunction (x, y) return x + y end if exampleFunction(10, 20) > 25 then print("test") end
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