[SOLVED] two more beginner lua questions

[AaronV]

#1 how do I do a for loop with a list of numbers i want to use?
i tried something like the following but I'm not sure what i did wrong

Code: Select all

for x in {42,20,6} do
 print x
end

should run three times printing 42, then 20, then 6

not sure I got the "print" part right but other than that...
is that not the code for a for loop over items in a list?



#2 how do I make and use the . operator? i want to work with variables like S.Length.
is this different than S[Length]? Is S[n] for integers only, like arrays?
Whats the difference between S = { this=5 } and S={}; S.this = 5. Can I even do either of those?



I'm sorry to ask such novice questions over the forums, but I can't seem to find any good answers.

[Santos]

#1:

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for index, value in ipairs({42, 20, 6}) do
    print(value)
end

index and value can be any two names you want. A common idiom in Lua is to use the name _ for values which won't be used.

Also, you if you call a function with a single literal table like in the code above, you can remove the opening and closing parentheses, if you find that easier to read.

Code: Select all

for _, x in ipairs{42, 20, 6} do
    print(x)
end

#2:

S[something] works for strings as well as integers. Be sure to use quotes when using strings. Using the . is simply "syntactic sugar". For example...

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S = {}
S["Length"] = 1000   -- Notice the quotes! Also, because this is preceded by "--", this is a comment.
print( S.Length ) -- This will output "1000".
print( S["Length"] ) -- This will also output "1000". This line is exactly equivalent to the above line.

You might want to check out some Lua tutorials. EDIT: Like Qcode said below this post, this forum is for all questions. I hope this doesn't seem like "read tutorials instead of asking questions!", I think asking questions is perhaps the best way to learn, I just wanted to share some resources which might be able to answer your questions quicker. Just... just thought I'd say this, just in case.

Hope this helps!

EDIT: OOPS! Thanks again Robin, sorry about that, I will try to take more care with my answers.

[AaronV]

okay that helps a bunch but I have a quick follow up question...

what would index be? what would I want to use it as? is it the list?

and i can say

S = {}
S.this = 5

right? cuz that would be awesome.


normally i test these things but I can't just hit compile.
i dunno, maybe i shouldn't rely on forums for easy questions.

[Qcode]

This is what the support forum is for, helping with questions, no matter what the difficulty is. Yes the s = {} s.this = 5 works.
Edit: Just saw your comment about the index. The value is whatever it returns as. In Santos's example thats a number though it could be a string or other values. The index will return whatever number this value is. Again in Santos's example the index of 42 would be 1 as its the first value. 20 would be 2 and 6 would be 3.

[AaronV]

so its kind of as if

Code: Select all

for i = 1, 3, 1 do
 ...
end

has an index of 1 and it's in ipairs{1,2,3}?
is that the right way to think about it?

so could i just say 42 instead of index/_?

just like the starting position? and if I wanted to use just the second one, how would i do that?
like if i didn't know what it was, i guess i would have to create a table (how else would i not know what it was) and then use table[2]...

i dunno, i've read a lot of tutorials on tables but i'm still kind of lost on the whole thing. which pretty much is the jist of lua.

[Robin]

Santos, you forgot the "do" for every for loop.

so its kind of as if

Code: Select all

for i = 1, 3, 1 do
 ...
end

has an index of 1 and it's in ipairs{1,2,3}?

It has the same effect as

Code: Select all

for i, _ in ipairs{1,2,3} do
 ...
end

if that's what you want to know.

so could i just say 42 instead of index/_?

No. 42 is not a variable name.

[AaronV]

oh my god now i'm even more confused.
sorry sorry sorry i'm super bad at programming i guess!

Code: Select all

a = 1
b = 2
for a,b in ipairs{1.0,2.0,3.0} do
 print (a)
 print (b)
end

would print out
1, 1.0 or
1.0, 1.0 or
1.0, 2?

also does anyone know of an IDE with a debug button for LUA?

[josefnpat]

oh my god now i'm even more confused.
sorry sorry sorry i'm super bad at programming i guess!

Code: Select all

a = 1
b = 2
for a,b in ipairs{1.0,2.0,3.0} do
 print (a)
 print (b)
end

would print out
1, 1.0 or
1.0, 1.0 or
1.0, 2?

also does anyone know of an IDE with a debug button for LUA?

This is what happens when I run your code... (hint hint)

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[~]$ lua
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> a = 1
> b = 2
> for a,v in ipairs{1.0,2.0,3.0} do
>> print(a)
>> print(b)
>> end
1
2
2
2
3
2

If you want to know what happens here, I can explain it:

basically, you assign b = 2 in a loop that traverses over 1,2 and 3. Here is your output annotated.

1 -- current index from your ipairs
2 -- b
2 --current index from your ipairs
2 -- b
3 -- current index from your ipairs
2 -- b

[AaronV]

your code says for a,v.
mine said for a,b.

does that mean that mine will only loop twice?

starting number in table, variable representing number in table

right?

or is it starting location in table?

[Robin]

No. Names are names, they don't mean anything specific.
i stands for index.
v stands for value.
You can use any name you want.

If you try this:

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for i, v in ipairs{"x", "y", "z"} do
   print(i, v)
end

It will print:

Code: Select all

1   x
2   y
3   z

Do you understand it now?