porquê não
When you answer a question, is it ok to use "porquê não" with the meaning of "yes"? (like "why not" in english

Question

Answer

"Porquê não" can be used to answer "yes" in some cases only, but is used in interrogative form: "porquê não?"
an example:
- Você vai trabalhar amanhã?
- Porque não? - But is common already say the affirmative : "Claro,porque não?" or "Sim,porque não?"
I believe that I gave correct answer,I think XD.

Answer

yes, you may use "Por que não" (notice Por separated from que) meaning yes.

The reason I used "Por que" and not "porquê" is because the interrogative pronoun is this. "porquê" is used when it works as a noun. For example: 
Pai, por que não posso sair? (Dad, Why can't I go out?)
porque está chovendo. Este é o porquê. (because it's raining. that's the Why)
Notice also that when you answer you use porque

Answer

You're right! It means "why not".

Answer

Are you asking about the use of " why not" instead of yes?

Ne manquez pas cette occasion d'apprendre une langue depuis chez vous. Découvrez notre sélection de professeurs de langues expérimentés et inscrivez-vous dès maintenant à votre premier cours !