How do you convert Byte Array to Hexadecimal String, and vice versa, in C#?

This is probably a common question over the Internet, but I couldn't find an answer that neatly explains how you can convert a byte array to a hexadecimal string, and vice versa.

Background-color hex to JavaScript variable (jQuery)

I'm kind of new to JavaScript and jQuery and now I'm facing a problem:

Objective C parse hex string to integer

I would like to know how to parse a hex string, representing a number, in objective c. I am willing to use both an objective, or a C based method, either is fine.