Lǎo tóngxué, hǎojiǔ bújiàn, nǐ yìdiǎnr dōu méi biàn.
Long time no see, old classmate! You haven't changed a bit.
Tips
usage
The everyday greeting for anyone you have not seen for a while, friends and colleagues alike; the usual answer is to say it back. 久违 means the same but sounds more literary, and also works for things: 久违的阳光 "sunshine we have not seen for ages".
culture
The English "long time no see" is often traced to this phrase, a word-for-word rendering of 好久不见 that passed into English through Chinese Pidgin English.
