Also, is there a difference between "спокойной ночи" and "доброй ночи"?
What we wish before going to bed is спокойной ночи (good night but to be precise "quiet night"). Доброй ночи ("kind " meaning "good and quiet ") is the same, but to my mind sounds poetically. But perhaps it's personal. The phrase is an abbreviation from
Я желаю вам/тебе спокойной/доброй ночи.
So желаю (чего?)+ genitive case (добрая ночь nominative – доброй ночи genitive).
Доброе depends on the gender of the noun, which this adjective agrees to. For example
Утро is of neutral gender (
Оно моё утро), so we should use
День is of masculine gender (
Он мой день), so we use
Доброй is slightly more complicated, as V.V. already stated, it is in genitive case with feminine noun. To summarize, please take a look at this table
| Masculine | Feminine | Neutral | Nominative | Добрый | Добрая | Доброе | Genitive | Доброго | Доброй | Доброго |
I should note, that usage of
Доброго вечера is allowed, but
Добрая ночь is incorrect