Countdown App 1, using os.time() and transition.to()

gistfile1.lua

--Countdown App

--os.time() returns the current number of  seconds since Jan 1, 1970 to current time
local start=os.time()
local background = display.newImage("background.png")
local W=display.contentWidth
local H=display.contentHeight
--timeIsUp is shown after time is Up, haha
local timeIsUp=display.newText("Time is Up!", 0,0, "James Fajardo", 100)
timeIsUp.x=W/2
timeIsUp.y=H/2
timeIsUp.isVisible=false --timeisUp is hidden at first. 

local function countDown(event)
  c = 10-(os.time()-start) --for every second, the difference will increase by one between os.time() and start
	cText = display.newText(tostring(c), 0, 0 , nil, 100)
	cText.x=W/2
	cText.y=H/2
	transition.to(cText,  {time=100,  alpha=0}) --when c changes, it changes smoothly by fading away in 100 miliseconds
	if(c==0) then --countdown is over
		--cleaning time, save some memory
		cText:removeSelf()
		c=nil
		timeIsUp.isVisible=true --time to show up
		Runtime:removeEventListener("enterFrame", countDown) --let's stop the enterframe show.
	end
end

Runtime:addEventListener("enterFrame", countDown)