Yes, Chiara. If you hold the stock before the ex-dividend date, you still have the right to get the dividend. if you buy the stock just after the ex-dividend date, you do not have the right to collect the dividend if it has not been paid.
We add 100 because, in one day, we will get a dividend of 100.
We add 100 because, in one day, we will get a dividend of 100.