huiping：考试的时候是不是不可以用简写啊（比如“u“）？
在ielts写作的时候是不是不可以用简写啊？

John：You shouldn't use abbreviations in the written exam.

Generally, abbreviations like that are only used in online chats or emails among young people, and usually only among close friends.  We wouldn't use abbreviations like "u" in any sort of formal communication.

心残游记0：so many thanks!!可以这样用吗??呵呵，没准是我自创的!
thanks a lot,John!u  gave me answers in detail!i will ask u more question when i meet them.these are for u as gifts! 
 
John：It's okay to say "so many thanks", but it's much more common to say simply, "many thanks".