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Learning Lua as a beginner

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Learning Lua as a beginner [ edit page ]

After reading this you should proceed with Learning Lua as a programer

Theory

Here we tell you the basics of Lua.

Variables

The type of a variable is set automatically depending on the value. Possible types are:

nil
boolean
number
string
function
table

myVariable = nil
myVariable = true
myVariable = 3.141
myVariable = {"a","b","c"}

Numbers are always saved as floats (double precision). So "3" is actually saved as something very similar to "3.00000001". Comparison will of course work:

(3 == 3.000000001) --true

Comments

comments are not executed:

-- this is a single line comment 
a = 1 + 2 -- this is also a comment, but the code before "--" will be executed

--[[ this is a multiline comment 
for long comments it makes sense to use it, instead of prefixing every line with --
still part of the comment
]]--
a = 1 + 2 -- this is also a comment, but the code before "--" will be executed

Math calculations / Arithmetic

myVariable = 1 + 2
myVariable = 2 - 1
myVariable = 2 * 4 -- multiplication, 2*4 = 8
myVariable = 9 / 4 -- division, 9/4 = 2.25
myVariable = 9 % 4 -- rest after a division, 9/4 => 2*4 + 1, so finally 9%4 = 1
myVariable = 2 ^ 3 -- 2 powed by 3, 2^3 = 2*2*2

Strings

myTextA = "Hello:"
myTextB = "World"
myText = myTextA .. myTextB -- myText = "Hello:World"
myText = "Number: " .. 1 -- myTExt = "Number: 1"

Tables

Each entry of a table is a combination of a key and a value. The key can be a number or a string. If you do not specify a key for a value, lua will automatically use numbers as keys. If you specify a key, this key will be not be visible in a "for" loop (see Loops) and it will not count in #table (length of table).

myTableA = {"a","b"} -- myTableA[1] = "a", myTableA[2] = "b"
myTableB = {x="a"} -- myTableB["x"] = "a", myTableB.x = "a"
myTableC = {"a",x="b"} -- myTableC[1] = "a", myTableC.x = "b"

Lua calculates the length of a table by starting at table[1] and then counting up until the last table[i] that is not nil. So table={"a","b",nil,"c"} -- #table = 4 but table={"a","b",nil} -- #table = 2

#myTableA --  length of myTableA = 2
#myTableB -- length of myTableB = 0
#myTableC -- length of myTableC = 1

if / else

This is used to execute different code depending on a condition. Any variable or expression can be used as a condition:

true => true 1 > 2 => false -- greater than 1 < 2 => true -- less than 2 == 2 => true -- equal 3 >= 2 => true -- greater or equal 3 <= 2 => false -- less or equal

nil => false -- nil equals to false, anything else (tables, numbers, string) ALWAYS equal true {} => true -1 => true "" => true

you can combine expressions with the keywords "not", "and", "or"

false or true => true false and true => false not true = false

(false or true) and true => false (false and true) or (true and true) => true

Functions

functions do some stuff and maybe return a value. They can accept input values, so called arguments:

function myFunction(argument1)
	return argument1 + 1
end

Loops

The "while" loop:

myTable = {true, true, true, false}
i=1
while i < 2 do -- as long as the i < 2 the loop will run, if that is not the case, the loop will exit.
	-- this line is called twice
	i = i + 1
end
-- i is now 2

Similar to the while loop is the "for" loop. It can do exactly the same (increment a number):

for i=1,2 do
	-- this line is called twice
end

You can manually set a step for the loop:

for i=1,2,0.5 do
	-- this line is called 4 times
end

And you can choose a different max, even negative (but dont forget to choose a negative step too).

for i=1,-5,-1 do
	-- this line is called 7 times
end

You can also loop over the entries of a table:

myTable = {"a","b","c"}
for k,v in ipairs(myTable) do
	-- this line will be called 3 times:
	-- 1. k=1, v="a"
	-- 2. k=2, v="b"
	-- 3. k=3, v="c"
end