How to implement decrement resource over time? (solved)

Questions
1

Let say if i have variable food = 100 , I want to decrease it -1/sec. So it will empty in 1 minutes 40 sec.
What I think is code like this :

function init(self)
  food = 100
end

function update(self, dt)
  food = food - 1  -- I know this code is wrong
  if (food == 0) then
    print("i'm die")
  end
end

How to implement that?

2

dt (deltatime) that is passed into update is the time that has passed since last update.
In this case you could easily do: food = food - dt

Now that will give you floating numbers of food so when representing food you might want to do math.floor(food)

Also use food =< 0.

3

Working very well thanks.