Functional Programming

Read this introduction to functional programming, through Section 3.3.1. As you will see from the article's index, many languages support functional programming, including (although not mentioned in the article) C/C++.

3. Concepts

A number of concepts and paradigms are specific to functional programming, and generally foreign to imperative programming (including object-oriented programming). However, programming languages often cater to several programming paradigms, so programmers using "mostly imperative" languages may have utilized some of these concepts.