Lua - Beginners Guide

Printing

print("Hello World")

Comments

--this is a comment
print("hello") --this is another comment
-- the next line will not do anything because it is commented out
--print("world")

Variables

-- Different types
local x = 10 --number
local name = "john doe" --string
local isAlive = false -- boolean
local a = nil --no value or invalid value

Numbers

operators

+ addition
- minus
* multiply
/ divide
^ power
% modulus

-- examples
local a = 1
local b = 2
local c = a + b
print(c) -- 3

local d = b - a
print(d) -- 1

local x =  1 * 3 * 4 -- 12
print(x)

local y = (1+3) * 2 -- 8
print(y)


print(10/2) -- 5
print (2^2) -- 4
print(5%2) -- 1

print(-b) -- -2

-- increment
local level = 1
level = level + 1
print(level) -- 2

Strings

-- concatenate strings
local phrase = "My name is "
local name = "John Doe"
print(phase .. name) --My name is John Doe

-- strings and numbers
local age = 12
local name = "Billy"
print(name .. " is " .. age .. " years old")

Boolean

local isAlive = true
print(isAlive) --true
isAlive = false
print(isAlive) --false

Conditional Statements

--number comparisions
local age = 10
if age < 18 then
  print("over 18") --this will not be executed
end

--elseif and else
age = 20
if age > 18 then
  print("dog")
elseif age == 18 then
  print("cat")
else
  print("mouse")
end

Comparison Operators

== equality
< less than
> greater than
<= less than or equal to
>= greater than or equal to
~= inequality

--boolean comparision
local isAlive = true
if isAlive then
    print("dog")
end

--string comparisions
local name = "billy"
if name == "Billy" then --false
  print("Billy")
elseif name == "billy" then --true
  print("billy")
end

Combining Statements

local x = 10
if x == 10 and x < 0 then --both are true
  print("dog")
elseif x == 100 or x < 0 then --1 or more are true
  print("cat")
end
--result: cat

Nested statements

local x = 10
local isAlive = true
if x==10 then
  if isAlive == true then
    print("dog")
  else
    print("cat")
  end
end

Invert Value

you can also invert a value with the not keyword

local x = 10
if not x == 10 then
  print("here")
end

Functions

function printTax(price)
  local tax = price * 0.21
  print("tax:" .. tax)
end

printTax(200)

--function that returns a value
function calculateTax(price)
  return price * 0.21
end

local result = calculateTax(100)
print(result)

--reusing the function but this time using variables
local bread = 130
local milk = 110

local breadTax = calculateTax(bread) --27.3
local milkTax = calculateTax(milk) --23.1

print("Bread Tax = " .. breadTax) 
print("Milk Tax = " .. milkTax)

--multiple parameters
function displayInfo(name, age, country)
  print(name .. " is " .. age .. " years old and is from " .. country)
end

displayInfo("Billy", 12, "Jupiter")

Scope

Variables have different scopes. Once the end of the scope is reached the values in that scope are no longer accessable

function foo()
  local a = 10
end

print(a) --nil

local isAlive = true
if isAlive then
  local a = 10
end

print(a) --nil

Global Variable

local _G.myValue = 69
--doing this can sometimes be bad practice

Loops

There is a few different ways you can do a loop in lua

--while loop
local i = 0
local count = 0

while i <= 10 do
  count = count + 1
end

print("count is " .. count) --count is 7


--for loop
count = 0
for i=1, 5 do
  count = count + 1
end
print("count is " .. count)

Infinite Loops

--infinite loop will never end
local i = 0
while i >= 0 do
 i = i + 1
 print(i)
end

Nested Loops

local count = 0
for a=1, 10 do
  for b=1, 10 do
    count = count + 1
  end
end
print(count) -- 100

Tables

--basic table
local colors = { "red", "green", "blue" }

print(colors[1]) --red
print(colors[2]) --green
print(colors[3]) --blue

--using a loop to iterate though your table
for i=1, #colors do
  print(colors[i])
end

Table Manipulation

--insert
local colors = { "red", "green", "blue" }
table.insert(colors, "orange")
local index = #colors --4 (this is the last index in the table)
print(colors[index]) --orange

--insert at index
local colors = { "red", "green", "blue" }
table.insert(colors, 2, "pink")
for i=1, #colors do
  print(colors[i])
end
--red, pink, green, blue

--remove 
local colors = { "red", "green", "blue" }
table.remove(colors, 1)
for i=1, #colors do
  print(colors[i])
end
-- "green", "blue"

2 Dimensional Table

--tables within tables
local data = {
  { "billy", 12 },
  { "john", 20 },
  { "andy", 65 }
}

for a=1, #data do
  print(data[a][1] .. " is " .. data[a][2] .. " years old")
end

Key Tables

2 dimensional tables are not suited to data with different types, instead uses keys for tables

local teams = {
    ["teamA"] = 12,
    ["teamB"] = 15
}

print(teams["teamA"]) -- 12

for key,value in pairs(teams) do
  print(key .. ":" .. value)
end

--insert into key table
teams["teamC"] = 1

--remove key from table
teams["teamA"] = nil

Returning a Table from a Function

This can be used to return multiple values from a functions

function getTeamScores()
  local scores = {
    ["teamA"] = 12,
    ["teamB"] = 15
  }
  return scores
end

local scores = getTeamScores()
local total = 0
for key, val in pairs(scores) do
  total += val
end
print("Total score of all teams:" .. total)

Math

The math class has a number of functions for dealing with numbers. You may not need them but here is some of the more useful one functions:

More: Wiki

abs (absolute value)

local x = -10
print(math.abs(x)) --result: 10
local a = 10
print(math.abs(a)) --result: 10

ceil (round up decimal value)

local x = 1.2
print(math.ceil(x)) --result: 2

deg (Convert value from radians to degrees)
```
print(math.deg(math.pi)) -- result: 180
```

floor (round down decimal value)

local x = 1.2
print(math.floor(x)) --result: 1

pi (constant value of pi)

print(math.pi) --3.1415926535898
3.1415926535898

rad (Convert value from degrees to radians)

print(math.rad(180)) --result: 3.1415926535898

random (random number generation)

--random value between 0 tand 1
print(math.random()) --result: 0.0012512588885159

--random integer value from 1 to 100 (both inclusive)
print(math.random(100)) --result: 20

--random integer value from 20 to 100 (both inclusive)
print(math.random(20, 100)) --result: 54

sqrt (Square root of a number)
```
print(math.sqrt(100)) --result: 10
```

Modules

Include code other files

require("otherfile")

fravemel/Lua-Beginners-Guide