"- What are you going to do this weekend? - Haven't decided yet, why?" is this correct?
I have a question on how to answer:

- What are you going to do this weekend?
- Haven't decided yet, why?

Is it ok to use "why" here to express that why he asked what am I going to do?
And can I use "What's up" or "What" to ask what is he going to say?

Thank you!

Question

"- What are you going to do this weekend? - Haven't decided yet, why?" is this correct?
I have a question on how to answer:

- What are you going to do this weekend?
- Haven't decided yet, why?

Is it ok to use "why" here to express that why he asked what am I going to do?
And can I use "What's up" or "What" to ask what is he going to say?

Thank you!

Answer

It's correct and people would understand what you mean. However, I think it's a little bit rude or something like that asking "why". You could say "Why? Have you already decided?". Well, I think it's better! At least, I think so.

Answer

"I havent decided yet, why?" Is completely correct. Adding why to the end is the perfect way to express that youre curious as to why they asked that question.

You could also say; "i havent decided yet, why, whats up?" Meaning essentialy the same thing. "Why, whats up?" Meaning "why are you asking, what are your plans?"