How can I separate paragraphs in comments? Is such a feature provided for comments? Sometimes I need to write a piece of code in comments and that's when I really need to separate lines from each other, but it seems that I can't do it in comments.
Comments were not really designed for this. If you need to add code, consider editing your initial answer (if applicable), or write your own answer. If it's just a short snippet, I'm sure most people will understand what you're trying to say (unless the code is in Whitespace, in which case you're out of luck).
That way, the community can upvote/downvote your answer based on its value. If it's a comment, it can only be upvoted, which doesn't always say much.
Paragraphs and code snippets are not supported in comments.
If you need to write a piece of code, or even more then one paragraph, in comments, you're not using the system correctly. Major changes to a question/answer should be done as edits to the original question/answer, not as comments. The commenting feature is for extended discussion of a question/answer.
Meta is an exception, and often extended discussions lead to multiple comments by a single OP.