Difference between "What do you do?" "How do you do?" and "How are you doing?"

Question

One friend is asked me, “What do you do?” And, "How are you doing?”

I started thinking, what is the difference between these?

• "What do you do?"
• "How do you do?”
• "How are you doing?"

Answer 1

“How are you doing?” and “How do you do?” are questions asking about how someone is feeling, although “How do you do?” has a more formal register to it, and I wouldn’t expect to hear it very much in the US, except perhaps in a formal introduction.

As often as not, these two questions are used as a form of greeting, and the person asking the question isn’t necessarily looking for an answer to the question. However, that’s partly contextual. If I’m recovering from surgery, and a nurse asks, “How are you doing?” I’ll assume the nurse wants to know if I’m in pain or not. If I’m walking down the hallway and a coworker asks, “How ya doin’?” as he’s passing by, I’ll assume it’s just a friendly greeting, and answer with something like, “Good, and you?”

On the other hand, “What do you do?” is a question that’s usually meant to ask what you do for a living. In other words, the person could ask, “What kind of work are you in?”

I wouldn’t expect to hear both questions asked without an answer exchanged in between them. So, a dialogue might go something like this:

"Hello, how do you do?"
"I’m doing fine, thank you. And you?"
"Quite well. May I ask, what do you do?"
"I’m a carpenter."
"Well, it sure must be nice that the weather is getting warmer.”

That dialogue shows what your questions mean, but it’s more formal than most friendly introductions might be. In a more informal setting, that conversation would sound more like this:

“Hey, how’s it going?"
“Pretty good – you?"
“I’m fine, thanks. You know, I just realized, I don’t know what line of work you’re in."
“Oh, I’m a carpenter."
"Well, you must appreciate this nicer weather we’ve been having.”

Answer 2

In the UK, there is a class element connected with the greeting "How do you do?". This greeting is formal. It is not meant as a question and an answer is not expected. The "correct" response is to say "How do you do?" back. Saying "Fine, thanks" might be seen as a sign of ill-breeding or lack of education. It is a subtle social indicator.