Tell me the difference between object oriented and functional programming ?
In object oriented programming, you define objects with "fields" that store data, and "methods" that manipulate those fields. An object oriented program is usually formulated imperatively, defining step by step instructions to complete the calculation.

In functional programming, you write the output mathematically, as a function of the inputs. A functional program is usually formulated in terms of "pure" functions which do not have "side effects" like writing to variables.