Can someone please explain "for" statements in lua?

[Janzo]

I've been using love for a little bit of time now, and i'm quite familiar with lua. However there is this one thing i have never grasped. Those freaking for statements.
i see things like

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for i = 1,100 do
blah blah blah
end

all the time, and i really can't seem to understand it
can someone explain it to me? thanks!

[CanadianGamer]

You can't iterate through an integer in lua. You can only loop through data types that support it such as tables.
For example.

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function love.load()
	--define example table
	exampleTable = {}
end

function love.update()

end

function love.draw()
	for i, enemy in ipairs(exampleTable) do
		--whatever it is you want to do with the information in exampleTable
	end
end

[Jasoco]

The example you posted simply means that "blah blah blah" will be executed 100 times in a loop. That's literally it.

[zorg]

You can't iterate through an integer in lua.

Bull.

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-- Simple numeric loop.
-- a is the number the loop should start at
-- b is the number it should end at (inclusive)
-- c is the step, meaning how many to add (or subtract, in case it's negative) from a until it reaches b. If you don't give this, it's 1 by default
-- i is the loop index, that changes inside the loop, that you can use there to keep track which iteration the loop is in.
for i=a, b, c do
  print(i) -- if a,b,c == 1,2,1 it will print two lines, 1 on the first, 2 on the second.
end

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-- A bit more advanced, this is an iterator, meaning it takes a table t, and goes through all the -numerical- indices inside (meaning all elements whose keys are in a sequence (meaning starting from 1, all following integers (whole numbers) until the first "gap")).
-- i is the current index of the table elements, that again, changes inside the loop body
-- v is the value that also changes, always equal to t[i]
local t = {'x','y','z'}; t[5] = 'w'
for i,v in ipairs(t) do
    print(i,v) -- will print the pairs 1,x; 2,y; 3,z; but since the 4th doesn' exist, it won't print the 5th.
end

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-- This is similar to the ipairs iterator above, but this will go through every existing key in a table, be it numeric or strings or anything else.
-- k is the current key, changing in the loop body as usual, basically same as the i index as above, but it can be almost anything.
-- v is similarly t[k], also changes in the body of the loop
local t = {}; t.abc = '1'; t.xyz = 1; t[50] = 'qwertz'; t[function() return 'whatever' end] = 'this works too'; t[true] = 'YES'
for k,v in pairs(t) do
    print(k,v) -- will print -all- of the above key,value pairs. the order is arbitrary!!!
end

All of the above work.

[Jasoco]

One thing to remember about pairs though is that the order it runs through is not predictable. So don't rely on it to execute code in a specific order, even if you add items to the table in the same order every time. Even if your table includes a table.a, table.b and table.c, it may not do a, b, c. Then again it might. It's never guaranteed.

[airstruck]

I've been using love for a little bit of time now, and i'm quite familiar with lua. However there is this one thing i have never grasped. Those freaking for statements.

Lolz.

Have you tried reading the section of the Lua manual about for statements? It's only about a page long.

The Lua manual sometimes uses very concise language and packs a lot of information into just a few words, but it explains everything you need to know if you take the time to think about it and understand it. A thread like this isn't going to tell you anything the manual wouldn't already have told you. Seriously, read the manual.

[CanadianGamer]

You can't iterate through an integer in lua.

Bull.

None of the example you gave are iterating through integers.
If you try to iterate through an integer like 6 or 1100 you'll get an error.

[Nixola]

You can't iterate through an integer in lua.

Bull.

None of the example you gave are iterating through integers.
If you try to iterate through an integer like 6 or 1100 you'll get an error.

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for i = 1, 6 do print(i) end
for i = 1, 1000 do print(i) end
for i = 1000, 6, -1 do print(i) end

[CanadianGamer]

Bull.

None of the example you gave are iterating through integers.
If you try to iterate through an integer like 6 or 1100 you'll get an error.

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for i = 1, 6 do print(i) end
for i = 1, 1000 do print(i) end
for i = 1000, 6, -1 do print(i) end

I that's not what I mean by iterating through an integer.
I mean something like this:

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for i in 1100 do print(i) end

[Nixola]

I that's not what I mean by iterating through an integer.

This doesn't mean it's not.
(EDIT from here on)
Furthermore, that is exactly what OP wrote:

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for i = 1,100 do
blah blah blah
end

One more thing, you don't iterate over tables, you iterate over iterators. This:

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for i in 1100 do print(i) end

is as broken as this:

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for i in {"foo", "bar", 6} do print(i) end

Both will raise an error. Almost the same error, in fact. Attempt to call a number/table value.

Before you claim you have to use ipairs/pairs to iterate over a table, you can do the same with a number. You can even monkeypatch ipairs itself:

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do
  local oldipairs = ipairs
  ipairs = function(n)
    if type(n) == "number" then
      local i = 0
      return function() i = i + 1; if i <= n then return i end end
    end
    return oldipairs(n)
  end
end

for i in ipairs(6) do print(i) end
>1
>2
>3
>4
>5
>6

The numeric for loop form iterates over a number, the generic for loop form iterates over values returned by an iterator. You don't need a table, and in fact Lua includes at least two other iterators: [manual]io.lines[/manual] and [manual]string.gmatch[/manual].