computercraft build wall

term.write("Please enter the height of wall: ")
local h = tonumber(read())
term.write("Please enter the width of wall: ")
local w = tonumber(read())

local itemID = 1
for i = 1, w do
  for j = 1, h+1 do
    turtle.select(itemID)
    while (turtle.getItemCount() == 0) do
      itemID = itemID + 1
      if (itemID > 16) then
        break
      end
      turtle.select(itemID)
    end

    if (itemID > 16) then
      break
    end

    if (j == h+1 and i % 2 == 1) then
      turtle.up()
      turtle.place()
      turtle.down()
      turtle.placeUp()
      break
    elseif (j == 1 and i % 2 == 0) then
      turtle.up()
      turtle.place()
      turtle.down()
      turtle.placeUp()
    elseif (j == h+1 and i % 2 == 0) then
      break
    end

    if (i % 2 == 1) then
      turtle.place()
      if (j < h) then
        turtle.up()
      end
    else
      turtle.place()
      if (j < h) then
        turtle.down()
      end
    end
  end

  if (itemID > 16) then
    break
  end

  if (i == w) then
    while (not turtle.detectDown()) do
      turtle.down()
    end
    break
  end
  turtle.turnRight()
  turtle.forward()
  turtle.turnLeft()
end