What is the difference between "¿qué haciendo?" and "¿qué estás haciendo?" Do they mean 'How are you doing?'
¿Qué haciendo, loco?
¿Qué estás haciendo, loquillo?
"¿Qué haciendo?" could be some type of expression typical from South America, although I've never heard it before, it could be some derivative from "Spanglish".
"¿Qué estás haciendo?" is the correct form in Spanish to ask "What are you doing?"
"¿Qué haciendo?" Is not a correct sentence in Spanish. It may be slang, but not proper Spanish. It lacks a verb.
I have occasionally seen the phrase
I don't suggest using, ever. Even in these informal contexts....
Unless ur goal iz 2 mock the ppl who talk that way, or 2 B ironic. U will B h8ed.
If you want to see the short answer, scroll down.
Long answer: Spanish is a complex system, a complex language. It's spoken in lots of countries in about three continents. In every single country –what is even more, every region in every country– Spanish develops independently. To deem idiotic (as other answer did) or erroneous an expression, implies that the person who produces that judgement has lived and understood every single kind of Spanish.
What does it mean? It doesn't have a verb either. But if you are intelligent you'll figure out soon that it's a nice greeting there.
In the same line of thought:
is a translation you could find for how you doing? (but that's definitely not it's origin). I dare to say that ¿Qué haciendo? is even "less incorrect" than whatcha doin'? – even so, absolutely grammatically incorrect if you see it as part of formal writing standing for the meaning "what are you doing?". But the phrase doesn't mean that: It's just slang and means "Hi!"
The difference between "¿qué haciendo?" and "¿qué estás haciendo?" is that the former means just hi! ̣–at least in Mexico– while in the latter you actually expect an answer from your interlocutor (everywhere). The loco or loquillo part actually I've heard it from Central America. It means just "dude!, buddy!". All in all, the former means "hi buddy!".
Again, it's slang. Be tolerant; if you don't like it or you are not an expert, don't use it.