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Lua: for beginner

The begin

• What is Programming?
• The Editor
• Variables in Lua
• LUA - Mathe
• Comments - Keywords
• Operations of Comparison / Logical Operations
• Chunks / Blocks
• Strings
• Loops
• Conditional Structures
• Tables
• Functions

the advanced

• The generic for

Lua - Functions

• Basic Functions
• table

The other

• Different Editors
• Pacman for LuaX with SDL

To use Lua in C

• Hallo World with Lua

Links

• Different games which are using LUA
• Links in german
• Links in english

We are able to read out a numerical table like

myTable[number] with a regular for-loop.

However, with such a kind of loop we would not succedd in reading out tables like:

myTable.myName

But this is exactly the ability of the generic for - loop.

for variable, value in pairs(table) do -- since Lua 5.1 the function pairs has to be used
-- chunck
end

Note:
The function pairs(table) returns the function next followed by the table.
We would also be able to write:

for variable, value in next,table do
-- chunck
end

Regardless if we have a numerical table or a table with names, this generic for-loop traverse every value of the table.

Example: We create a table with every week day

days = {"Sunday", "Monday", "Tuesday","Wednesday",
"Thursday", "Friday", "Saturday"}

Now we have a table as follows:

days[1] = "Sunday"
days[2] = "Monday"
days[3] = "Tuesday"
days[4] = "Wednesday"
days[5] = "Thursday"
days[6] = "Friday"
days[7] = "Saturday"

days is a numerical table

Now it's time for our generic loop. We do not have to know the table size as every value will be traversed until we get a nil-value.

numberforDay = {} -- new table
for variable, value in pairs(days) do
numberforDay[value] = variable
end


Explanation:

• we create an empty table (numberforDay)
• the loop traverse every value of the table days
• in every cycle the variable (called variable in our example) gets the value which is addressed. In our case these are the numbers [1...7]
• in every cycle the variable (called value in our example) gets the value of the according number [Sunday ... Saturday]
• finally the chunck creates a new part of the table numberforDay like as follows:

numberforDay.Sunday = 1

.....

numberforDay.Saturday = 7



Now we are going to check this in the editor (because we also want to see what we have read)



Due to the loop:

for i,v in pairs(days) do
numberforDay[v] = i
end

we also see, that there exists another kind of creating a table with names

numberforDay.Sunday = 1 -- we already know
numberforDay["Sunday"] = 1 -- we have just learned
numberforDay = {Sunday = 1} -- is possible as well



Do you also agree that this is really versatile? We only need to use it according our demand.