Sometimes, we need to look on other's code to understand a concept. The easiest way is by looking at books that talks about programming languages. Unfortunately, people find it too hard to buy a book, mostly because it's written in English and it's quite expensive.
So here's one of the solution: codefetch. Just enter the topic you wanted to know, and it will display the code from several programming books. Beware as it might not show the whole code, but just a little portion of it (except when the function is small enough).
They also provide a link on each function to the manual page of each programming languages, suitable for learning what the function is there for. Here's an example of PHP code