about Engish grammer

You'd better not use this sentence'long time no see'.It is very strange.You can say 'What's up' when you encounter an acquaintance.Or 'What's going on?''Sup dawg?'That will be fine.

Yes, you can use that expression. It is somewhat dated, but i still hear native speakers use the expression. "Hi" is, i believe, used only in North America. It would not be unusual to hear and American or a Canadian say: "Hi, how are you? Long time, no see."

Abby 1213 is giving bad advice, and is not a native speaker, i suspect. "What's up" is a common enough greeting--i doubt that many native speakers would use "What's going on" as an initial greeting. "Sup dawg" is hilarious--that's the slang of a younger generation of Americans of African descent, and it, too has become dated. I advise you not to use that expression as a greeting.

ah,i thought it just an informal way of greeting to somebody in China. i didn't thought that people in North America would use it usually.Because there is a scentence- 好久不见 in China whose meaning is the same as the scentence i said. So, i can use it orally andi'd better not to use it when i am writing letters,right?

No, you would not want to use that in a letter. "Hi, how are you? Long time no see." is perfectly acceptable in conversation.

Hi.You are right.I'm not a native speaker and Kathy is my friend actually.I'm glad to see your comment.To tell you the truth,I learnt those sentences from a Talk Show in China.The host is an American.He usually uses the slang.What do you think of the slang.I'm very confused wheather I should use slang.

Slang is acceptable in conversation. It should not be used in written English, unless you are writing a novel or a short story in which the characters speak that way. Without wishing to offend, I don't think your English is good enough for writing stories or novels. I also think that you need to have a much better command of the language to use slang in the same way that a native speaker would use slang.

Another point about written English: you should leave a space after using a comma, and two spaces after the end of a sentence.

Oh, thank you. You are very nice.

In my opinion，some famous English grammarians have put this phrase into the English dictionary，so i think you can use it. Besides，i think in our daily spoken English，we don't need to be so strict with this.

No, it looks so weird.

But why ?

It's no longer common usage in the United States to put two spaces after a period. One is fine.

I disagree, which is my privilege. Furthermore, even with the new technology, there are still compositors, and they leave a greater space after the end of a sentence in printed works.

Absolutely your privilege, set.

Here's what the Chicago Manual of Style has to say on the matter. (This is the source I'm required to use for my work.)

Published work these days rarely features two spaces after a period. In the era when type was set by hand, it was common to use extra space (sometimes quite a bit of it) after periods, a practice that continued into the first half of the twentieth century. And many people were taught to use that extra space in typing class. But introducing two spaces after a sentence-ending period—and only after those periods—causes problems. Absolute consistency is easy to monitor when double spaces are never allowed, but less easy when some spaces after periods are double and others single (such as those at the ends of abbreviations and initialisms in running text). Since there is no proof that an extra space actually improves readability—as your comment suggests, it’s probably just a matter of familiarity—CMOS follows the industry standard of one space after a period.

I did not say that two spaces are required after a period. I said after the end of a sentence--it would apply to a sentence ending with a question mark or an exclamation point as well. As i pointed out, compositors still leave a larger space after the end of a sentence than that which is left between words.

You think your way, and i'll think mine.

You're right. Any punctuation at the end of a sentence. However, I don't see where compositors are relevant to the situation. The OP seemed to be referring to personal communication.

I'll continue to think my way, and you continue to think yours. Fact is, this is a matter of preference.

Certainly it's a matter of style.

Both 'Hi,' and 'Long time no see,' are used in the UK, and have been for as long as I can remember.

I didn't know that "Hi" was used there, so i didn't want to claim to know what i did not know.

By the way, i did not claim that "long time, no see" was used only in North America. So, you know, got try to take the piss with someone else.