Every time a (rated) round ends, I always see the same questions from people who are new to Codeforces. So, here I made an FAQ that answers to these repeated questions. Please do provide the link to this blog when you want to answer to them.
Why is my rating still not updated yet?
Be patient. It takes a while (can be a few hours, or even more) to finalize things such as detecting cheats and confirming test results, or there can be other issues that need investigation. It won't be unrated unless they announced that it will be unrated.
My solution was hacked after contest, but why didn't my rank / rating change?
It is called uphacking, and it does NOT affect the standings nor rating changes. The score you gained from uphacked solution will remain. The hack tests will be added to the tests for practice submissions later, but there won't be any rejudges on already accepted solutions.
I got a system message that says that my submission coincides with other solutions, but I really didn't cheat.
Don't use online IDEs like ideone with public mode. Other people can read it! Make sure you're using private (needs to be signed in) or secret mode.
(Educational & Div. 3/4 rounds) It has been 10 hours after the contest, why is my rating still not updated?
For Educational & Div. 3/4 rounds, there is 12-hour open hack phase after the contest where anyone can read anyone's solutions and try to hack them. Unlike uphacking for standard rounds, successful hacks made during open hack phase WILL change their verdicts to hacked and they will be considered as incorrect submissions. Hack tests made during open hack phase will be added to main tests after the phase, and all the accepted solutions will be rejudged upon all original tests + hack tests and only the submissions that passed them all will be considered accepted.
(Educational & Div. 3/4 rounds) So the open hack phase has ended, but my rating still hasn't changed yet?
Again, be patient. They need time to add hack tests and run rejudges. After that, it can take a few more hours again.
Any suggestion to improve this FAQ is welcomed.