I have code written in any programming language. How can I "prettify" it (bold if, else etc.) to display on a website? Are there any good APIs to do that?
There is Google's prettify which is widely used for such tasks (e.g. SO itself uses it for highlighting of code).
Google Code Prettify JavaScript library supports all C-like (Java, PHP, C#, etc), Bash-like, and XML-like languages without need to specify the language and has customizable styles via CSS.
Moreover, as i know, there is a lot of third-party styles for those languages that not supported officially.