Mining Turtle - Stairs

local width = 1
local depth = 1
local height = 4
local upDown = ''

--Handy movement functions
local function upBy(num)
	for i=1, num do
	turtle.up()
	end
end
local function downBy(num)
	for i=1, num do
	turtle.down()
	end
end
local function leftBy(num)
	turtle.turnLeft()
	for i=1, num do
		turtle.forward()
		end
	turtle.turnRight()
end
local function rightBy(num)
	turtle.turnRight()
	for i=1, num do
		turtle.forward()
		end
	turtle.turnLeft()
end

local function digHeight()
	for i=1, height do
	turtle.dig()
	turtle.digUp()
	turtle.up()
	end
end

 local function stairsDown()
 	print("Witness me make a fine staircase that's " .. width .. " tiles wide, " .. height+1 .. " tiles tall, and goes down for " .. depth .. " levels");
	for d=1, depth do
		digHeight()
		downBy(height)
		-- Dig the horizontal width
		for i=1, width-1 do
			turtle.turnRight()
			turtle.dig()
			turtle.forward()
			turtle.turnLeft()
			turtle.dig()
			digHeight()
			downBy(height)
		end
		turtle.forward()
		-- Dig blocks beneath the horizontal width
		for j=1, width do
		turtle.digDown()
		turtle.turnLeft()
		turtle.forward()
		turtle.turnRight()
		end
		turtle.down()
	 end
end

 local function stairsUp()
 	print("Witness me make a fine staircase that's " .. width .. " tiles wide, " .. height+1 .. " tiles tall, and goes up for " .. depth .. " levels");
	for d=1, depth do
		digHeight()
		downBy(height)
		-- Dig the horizontal width
		for i=1, width-1 do
			turtle.turnRight()
			turtle.dig()
			turtle.forward()
			turtle.turnLeft()
			turtle.dig()
			digHeight()
			downBy(height)
		end
		turtle.forward()
		-- Dig blocks beneath the horizontal width
		for j=1, width do
		turtle.digUp()
		turtle.turnLeft()
		turtle.forward()
		turtle.turnRight()
		end
		turtle.up()
	 end
end

function main()
if turtle.getFuelLevel() <= 0 then
    print("WARNING: Fuel is empty!")
    end

print("Enter staircase width:")
	width = tonumber(read())
print("Enter staircase height:")
	height = tonumber(read())
print("Enter staircase depth:")
	depth = tonumber(read())
print("Stairs up or down? (U/D)")
	upDown = tostring(read())

	if string.find(upDown, 'u') or string.find(upDown, 'U') then
		stairsUp()
	elseif string.find(upDown, 'd') or string.find(upDown, 'D') then
		stairsDown()
	else
		print("ERROR: Invalid input, cancelling mining operation.")
	end

 end
 main()