Tower With Stairs v3

--CurrentLuaProgram.lua
print("Hello World")
--TurtleTower

--Check arguments for correct formatting
local args = { ... }
if #args ~= 1 then      --Check if it's not exactly 3 arguments.
    shell.run("clear")
    print("Invalid number of arguments")
    print("turtletower [height]")
    do return end
end
for i = 1, 1 do            --Step through each argument and make sure it is a number greater than 1.
    if tonumber(args[i]) < 2 then
        shell.run("clear")
        print("Invalid arguments")
        print("All measurements must be numbers greater than 1")
        do return end
    end
end
--------------------------------------------------

--commandline arguments [height]
length = tonumber(args[1])  --length of square
slotnum = 1
--------------------------------------------------

for i = 1, length do
    if not turtle.detectUp() then
        turtle.up()
    end
    for j = 1, 4 do
        for k = 1, 3 do
            if not turtle.detectDown() then
                if turtle.getItemCount(slotnum) < 1 then
                    slotnum = slotnum + 1
                    turtle.select(slotnum)
                end
                turtle.placeDown()
            end
            turtle.forward()
        end
        turtle.turnRight()
        turtle.forward()
    end
end
turtle.forward()
turtle.turnRight()
turtle.forward()
for i = 1, length do
    turtle.down()
end
turtle.turnRight()
turtle.turnRight()
turtle.dig()
turtle.up()
turtle.dig()
turtle.down()
turtle.turnRight()
turtle.forward()
turtle.turnRight()
for i = 1, length do
    turtle.up()
    turtle.forward()
    if turtle.getItemCount(slotnum) < 1 then
        slotnum = slotnum + 1
        turtle.select(slotnum)
    end
    turtle.placeDown()
    turtle.forward()
    if turtle.getItemCount(slotnum) < 1 then
        slotnum = slotnum + 1
        turtle.select(slotnum)
    end
    turtle.placeDown()
    turtle.turnRight()
end