Q:
Do the Google give warnings first before they ban the member?

A:
Depends on how many site are in your account and how much each is making.
If you have three sites, each making around $100 a day, then you would get a warning and maybe the site in question will be banned (not the account).
However, if you have one site, and it is in question and you have fifty others making nothing, then chances you entire account will be banned. unless what you did was heavily harmful, in most cases, they dont warn before banning.
If it is a minor TOS violation, you may (or may not) get a warning. If you try to cheat them, there will be no warnings, 100% ban.

Conclusion:
Try to invest a few hours in reading Google TOS and simple comply to the TOS precisely as published. Hence just be a clean and honest publisher and you have nothing at all to fear or worry.