Basic Bridge Builder

s = 2

n = 0



print("+-------------------------------------+")
print("| Bridge Maker                        |")
print("+-------------------------------------+")
print("| Slot 1: Fuel                        |")
print("| Slot 2-16: Building Blocks          |")
print("+-------------------------------------+")
print("| Place turtle facing towards desired |")
print("| direction. Insert fuel. Select      |")
print("| length. Press enter to start.       |")
print("+-------------------------------------+")
print("| Bridge length = ?                   |")
print("+-------------------------------------+")
l = tonumber(read())
turtle.refuel()

while n < l do
    turtle.select(s)
    if turtle.getItemCount() > 0 then

    else
        if s == 16 then
            l = n
        else
            s = s + 1
            turtle.select(s)
        end
    end
    turtle.forward()
    turtle.placeDown()
    n = n + 1
end

while n > 0 do
    turtle.back()
    n = n - 1
end