IPhone 5 Suddenly Can't Connect to Wi-Fi?

Just yesterday I can connect to any Wi-Fi area but by the afternoon I can't see any connection. Is it about the iPhone 5 or iOS 6.0.2?

That was a problem with the iphone 5 but the update should have fixed that. Try Factory resetting it? I guess.

IPhone 5 seems to have lots of errors.

Where did you use the Wi-Fi? In your own house or in public? If it is the public Wi-Fi, you might restart the iPhone and see if the Wi-Fi shows up, and if you can connect to it. If not, you might need to upgrade the iOS to 6.1, which might solve that.
If it is the Wi-Fi from your own router, you should do some set ups on it!