How to make optionals?

So I was making a disk that opens a door to the right and ejects itself. I want the ejection to be optional. How do I do this? Also, I want the user to input the "Yes" "No" for eject.

print( "Would you like to eject the disk? (Yes/No)" )
local opt
local cx, cy = term.getCursorPos()
repeat term.setCursorPos( cx, cy ) term.clearLine() opt = read():lower() until opt == "yes" or opt == "no"
if opt == "yes" then
    disk.eject( 'right' )
else
    print( 'okay :o/>' )
end

Use an if statement … the repeat loop is just for so it only continues until the user types yes or no

Thanks. This will be for the first AzhfTech: Keycard xP I will give some credit.

If you want it to be optional to wich side the redstone emits you have to put on your disk the program "mydoorside" and run this code ( or implement it in a way )

--first lets open the file we want to read > opening in reading mode, "r"
local file = fs.open("/disk/mydoorside", "r")
-- lets read the file:
local fileReader = file.readAll()
--And what you must never forget, close the file.
file.close()

-- Determine wich side to set the redstone output
if fileReader == "right" then
   redstone.setOutput("right", true)
   -- etc.
elseif fileReader == "left" then
   redstone.setOutput("left", true)
   -- etc
else
   print("The file is invalid to me")
end

Edit: wow.. I derped hard. I didnt read your message properly I guess, but anyway now you learned hopefully something about files..

Have posts above and you could do this
if you just want them to press a button

while true do
term.clear()
term.setCursorPos(1,1)
print("Would you like to eject the disk? (y/n)")
evt, p1 = os.pullEvent()
if evt == "char" and
p1 == "y" then
  disk.eject("right")
  print("Disk ejected!")
  sleep(2)
elseif p1 == "n" then
  print("Disk was not ejected!")
  sleep(2)
  end
   end