Protips: The little things you learn to pro up your French

In English, answers to both affirmative and negative questions take the same form:

‘Did you buy the cheese?’

‘Yes’

‘Didn’t you buy the cheese?’

‘Yes’ (implied: yes, I did buy the cheese)

In French, a positive response to an affirmative question is ‘oui’, while that of a negative question is ‘si’:

‘T’as acheté le fromage ?’

‘Oui’

But:

‘Tu n’as pas acheté le fromage ?’

‘Si’ (implied: si, je l’ai acheté)