ComputerCraft Turtle Wall Builder

--Author: MrPipa
--Place the turtle in the lower left corner in front of the wall
--Usage: <Name of the program> <height> <width>

local x,y = ...
h = tonumber(x)
l = tonumber(y)

--Preparations
    --Input check:
    print("Your input was:\nHeight: " .. h .. "\nWidth: " .. l)
    if h < 1 then
        print("Usage: wall <height> <width>")
        return
    end
    if l < 1 then
        print("Usage: wall <height> <width>")
        return
    end
print("Input ok!\nMaking necessary preparations...")

    --Minor fixes...
    slot = 0
    l = l - 1

    --Moving into place:
    turtle.forward()
    turtle.up()
    turtle.turnRight()
    while turtle.getItemCount() == 0 do
        if turtle.getSelectedSlot() == 16 then
            print("ERROR: Out of materials!")
            return
        end
        turtle.select(turtle.getSelectedSlot() + 1)
    end
    turtle.placeDown()

print("Preparations complete!")

--Building
print("Building...")
for i = 1,h do
    for i = 1,l do
        turtle.forward()
        while turtle.getItemCount() == 0 do
            if turtle.getSelectedSlot() == 16 then
                print("ERROR: Out of materials!")
                return
            end
            turtle.select(turtle.getSelectedSlot() + 1)
        end
        turtle.placeDown()
    end

    if i < h then
    print("Moving to next level...")
        turtle.turnLeft()
        turtle.turnLeft()
        turtle.up()
        while turtle.getItemCount() == 0 do
            if turtle.getSelectedSlot() == 16 then
                print("ERROR: Out of materials!")
                return
            end
            turtle.select(turtle.getSelectedSlot() + 1)
        end
        turtle.placeDown()
    end
end
print("All done!")