"I have to buy curry because there isn't any more left."
Translation:Je dois acheter du curry parce qu'il n'y en a plus.
J'ai besoin d'acheter. When "de" is followed by a vowel it becomes " d' " (D apostrophe). Also you need an apostrophe for "J'ai". An apostrophe in both these cases shows that a vowel has been taken away for an easier turn on the tongue. ie
Je ai = J'ai
Besoin de acheter = Besoin d'acheter