Will past offenses affect my citizenship application?

Did you plead guilty to the possession of marijuana?

Any drug charge can potentially impact your case. You need to contact experienced immigration counsel before you file your petition. It sounds like you had some type of conditional discharge on your marijuana conviction and the case shows a dismissal, however, it may be a conviction for immigration purposes.

My recommendation is that you seek the advice of a qualified immigration attorney. From your description, the more recent problem with marijuana is the more troubling, especially because it would appear to have occurred during the period for which you must establish that you are a person of good moral character. Keep in mind that cases which result in no action or even in the dismissal of charges after completion of a diversion program can still be used by CIS in determining whether you meet the good moral character requirement. CIS has become increasingly more and more difficult about approving cases where there is any problem suggesting any lapse of judgment questioning one's character. So best advice is to find someone who is qualified to discuss the concerns with you and who can provide some guidance on the possible issues that you may face in submitting the Form N-400. This case doesn't look like an absolute no. Instead an understanding that you may face issues with review of the case. Find someone good and you will be rewarded many times over by being placed in a position to make an informed decision.

If you served 40 hours community services, it probably means you are convicted of drug offense. and since it is within the past 5 years, your N400 application will most likely be denied for lack of good moral character.

If the marijuana case was dismissed, it will not affect you. The other cocaine charge could be used by immigration against you even though the case did not proceed in court. It is not very common but the law is out there that says that if immigration has reasons to believe that you were trafficking in drugs, even though no conviction and immigration have enough evidence, it could be used against you. It is up to immigration if they want to go that route.