Build Square V0.1

--Build Square V0.1 by QQII
--Declerations
local Arguments = { ... }       --Program arguments
local size = tonumber(Arguments[1]) or 0

--Functions
local function forward()        --Moves forward
    if turtle.getFuelLevel() == 0 then
        shell.run("refuel", "all")
        if turtle.getFuelLevel() == 0 then
            print("ERROR: out of fuel")
            read()
        end
    end
    while not turtle.forward() do
        turtle.dig()
        turtle.attack()
    end
end

local function inventory_sort()     --Fills the first slot with items from the other slots
    for i = 2, 16 do
        turtle.select(i)
        turtle.transferTo(1, turtle.getItemCount(i))
        if turtle.getItemSpace(1) == 0 then
            break
        end
    end
    turtle.select(1)
end

local function place_down()     --Places a block below the turtle
    while not turtle.detectDown() do
        while not turtle.placeDown() do
            inventory_sort()
            if turtle.getItemCount(1) == 0 then
                print("ERROR: out of items")
                read()
            end
        end
    end
end

local function line(l)          --Places a line of size l
    for i = 2, l do
        place_down()
        forward()
    end
    place_down()
end

--User Inputs
print("The turtle will build a square")
if size <= 0 then
    io.write("Size: ")
        while size <= 0 do
            size = tonumber(read())
        end
end

--Main Script
for i = 1, size do
    line(size)
    if i % 2 ~= 0 then
        turtle.turnRight()
        forward()
        turtle.turnRight()
    elseif i % 2 == 0 then
        turtle.turnLeft()
        forward()
        turtle.turnLeft()
    end
end