How to make GUI keep fading out and in ?

So umm i want this script just do fade in and fade out while true like its 0.50 background in the first time and then just goes to 1 transparency and 0.50 for the whole time, but it does not work! it just keeps going from 0.50 to -999

button = script.Parent

while true do
  for i = 1, 50 do
      button.BackgroundTransparency = button.BackgroundTransparency - 0.01
   wait(0.01)
if button.BackgroundTransparency == 0.50 then
     for i = 1, 50 do
      button.BackgroundTransparency = button.BackgroundTransparency + 0.01
   wait(0.01)
   end
  end
 end
end

thanks!

Sorry to say, but you may need to read up more on the for loops here.

First, if you haven't realized, but your for loops are WAY off.

for i = 1, 0.25 do

Above is a big NO NO! Never try this, it will not work, the smaller number, .25, MUST come before the larger number, 1.

Since your code isn't very effective, I'm going to start from scratch. First, we'll declare the button variable!

button = script.Parent

Simple right? Next, we'll add the infinite loop in the script.

button = script.Parent

while(true) do
end

That was easy too, but let's get to the part you weren't sure of! From what I understand you're attempting to go from .5 transparency to 1, back to .5 and then repeat that, yes?

button = script.Parent

while(true) do
	if(button.BackgroundTransparency <= 0.5)
		-- Code to move to 1
	else
		-- Code to move to 0.5
	end
end

Above we added a function to see if the transparency is less than or equal to 0.5, and if so, we'll make it go to 1, else it will go down to 0.5!

button = script.Parent

while(true) do
	if(button.BackgroundTransparency <= 0.5)
		while(button.BackgroundTransparency < 1) do
			button.BackgroundTransparency = button.BackgroundTransparency + 0.02
			wait(0.1)
		end
	else
		while(button.BackgroundTransparency > 0.5) do
			button.BackgroundTransparency = button.BackgroundTransparency - 0.02
			wait(0.1)
		end
	end
end

This is the finished code. The while loops ensure that the transparency is what we want it to be! Hopefully this will work, but I can't ensure it because I've been programming in Java for the past month, so I may have messed up!