Select next slot every other loop / Switch to next slot when slot is empty?

local i=1
x=tonumber(io.read())
turtle.select(1)
repeat
for f=1,32 do
turtle.placeDown()
turtle.up
end
i=i+1
until i == x

local i=1
local slotNum
x=tonumber(io.read())
turtle.select(1)
repeat
for f=1,32 do
if f%2 == 0 then
   slotNum = slotnum + 1
   turtle.select(slotNum)
end
turtle.placeDown()
turtle.up()
end
i=i+1
until i == x

local i=1
local slotNum
x=tonumber(io.read())
turtle.select(1)
repeat
for f=1,32 do
while turtle.getItemCount() == 0 do
   slotNum = slotnum + 1
   turtle.select(slotNum)
end
turtle.placeDown()
turtle.up()
end
i=i+1
until i == x

turtle.up()
turtle.select(1)
   local i = 1
write("How high should the dice be: ")
   x = tonumber(io.read())
turtle.forward()
--walls
for f=1,x do
for a=1,8 do
turtle.forward()
turtle.placeDown()
end

turtle.turnRight()

for b=1,8 do
turtle.forward()
turtle.placeDown()
end

turtle.turnRight()

for c=1,8 do
turtle.forward()
turtle.placeDown()
end

turtle.turnRight()

for d=1,8 do
turtle.forward()
turtle.placeDown()
end

turtle.turnRight()
turtle.up()
end

--Turtle going down when finished
turtle.back()
while not turtle.detectDown() do
turtle.down()
end

while turtle.getItemCount() == 0 do