program help

First off I wanna say i'm not big on writing code but I wanted to make a simple program to place cake above a turtle but I cant seem to get it to work when I run the startup.

http://gyazo.com/5f67596ba024334438d9e479cdd9786a

i'm trying to get it to place cake on top of itself when it detects nothing above it any ideas or help would be appreciated

You've got a very simple problem:

When 'turtle.detectUp()' is true, that means there IS something there.
You need to invert what it returns

if not turtle.detectUp() then
  turtle.placeUp()
end

If you'd like it to check every few seconds, instead of just when the computer starts,
you can do this:

while true do --# true will always be true, so it loops forever
  if not turtle.detectUp() then
    turtle.placeUp()
  end
  sleep(5) --# Waits 5 seconds
end