Learn Hardcore Chinese: tā wèishénme hái méi lái? wǒ xūyào zhǎo tā. nǐ děng le duōjiǔ? - Why hasn’t he come yet? I need to look for him. How long have you been waiting?

Use 没(有) to negate past or completed actions and to say something has not happened: 他还没来 = He hasn’t come (yet).
Use 不 for habitual, future intention, or general negation: 他不来 = He won’t come/doesn’t come.

What does 还 mean here, and where does it go?

Here 还 means “still/yet.” The fixed pattern is 还 + 没(有) + Verb: 他还没来. Don’t say 没还来.

Is 还没来 the same as 还没有来?

Yes. 还没有 is the full form; 还没 is the common shortened form. Meaning is the same.

What’s the difference between 还没来 and 还不来?

还没来: He hasn’t arrived yet (a fact about an event that hasn’t occurred).
还不来: He still isn’t coming/won’t come now (refusal, decision, schedule, or attitude).

Can I use 一直 instead of 还 (e.g., 他一直没来)?

Yes, but nuance differs: 一直没来 emphasizes “the whole time, continuously hasn’t come.” 还没来 emphasizes “not yet (but expected).”

Why use 为什么 and not 怎么? Can I say 他怎么还没来？

为什么 asks for a reason (neutral): Why…?
怎么 here means “how come,” often with surprise or mild complaint. 他怎么还没来？ is fine but more emotive.

Where can 为什么 go in the sentence?

Both are common:

他为什么还没来？
为什么他还没来？
Putting 为什么 first slightly foregrounds the reason; after the subject slightly focuses on “him.”

Do I add 吗 to a 为什么 question?

No. With a question word like 为什么, do not add 吗.

What does the 了 after 等 do in 你等了多久？

That 了 is the aspect marker showing the action occurred/has been ongoing for some time.

你等了多久？ can ask “How long did you wait?” (completed) or, in casual speech, “How long have you been waiting?”
To make “up to now” clear, say 你等了多久了？

Which is better: 你等了多久 or 你等多久了?

Both occur. Common guidelines:

Ongoing up to now: prefer a sentence-final 了: 你等了多久了？/你等多久了？
Completed in the past: 你等了多久？

Why is 多久 after the verb instead of at the front?

In Chinese, question words stay in their normal position. So it’s 你等了多久？, not “多久你等了？”

Is 多久 the same as 多长时间?

Yes for duration: 你等了多久(了)？ ≈ 你等了多长时间(了)？

How is 多久 different from 什么时候?

多久 asks “how long” (duration).
什么时候 asks “when” (a point in time).

Do I need 在 to show the progressive, like 你在等他吗?

Not in the duration question. With duration you typically use 了: 你等了多久了？
Use 在 for the simple “be doing” state: 我在等他。

What exactly does 找 mean in 我需要找他?

找 is “to look for; to try to contact/see.” It can imply seeking someone to talk to.
To emphasize success, use 找到 (“to find”): 我找到他了。

Should it be 我需要找他 or 我需要去找他?

Both are fine:

需要找他: need to look for/contact him (neutral).
需要去找他: adds “go (somewhere) to look for him,” emphasizing movement.

Can I use 要 instead of 需要?

Yes, but nuance shifts:

我需要找他 = I need to find him (clear necessity).
我要找他 can mean “I’m going to/I want to find him” (plan or desire). Context decides if it’s “need.”

Could I drop the second 他 in 我需要找他?

If context makes the object obvious, you can omit it in conversation: 我需要找（他）。 But keeping 他 avoids ambiguity and is more natural in isolation.

Does 来 always mean coming to where the speaker is? What about 到?

来 generally means “come (toward the speaker/here).” 他还没来 implies he hasn’t come here.
到 emphasizes arrival at a place: 他还没到 (not yet arrived—place may need to be specified: 还没到家/公司).

Should it be 他为什么还没到 instead of 还没来?

Both work, with nuance:

还没来: hasn’t come here (speaker’s location/event).
还没到: hasn’t arrived (at some location, often named).

What’s the difference between 他没来 and 他没来过?

他没来: He didn’t come/hasn’t come (this time/occasion).
他没来过: He has never come before (at any time up to now).

Can I add 呢 at the end, like 他怎么还没来呢？

Yes. Sentence-final 呢 softens or adds puzzlement/emphasis: 他为什么/怎么还没来呢？ feels more musing or concerned.

Can I say 他为什么再没来？ using 再?

No. 再 means “again/in the future (do again).” For “not yet,” use 还没(有): 他为什么还没来？

How do I express explicit durations?

Use: Subject + Verb + 了 + Duration + (了)

Ongoing: 他等了三个小时了 (he’s been waiting three hours and still is).
Completed: 他等了三个小时 (he waited three hours, then stopped).

“他/她” are both pronounced tā. How do I tell them apart?

In speech you can’t; context tells you. In writing, 他 = he/him, 她 = she/her.