This document discusses user-defined functions in C++. It covers topics such as value-returning functions, void functions, parameters, and function prototypes. Specifically, it explains how to define and call user-defined functions, the differences between value and reference parameters, and how memory is allocated for parameters. It provides examples of common function types like those that return values, take parameters, or have void return types. The goal is to teach readers how to construct, use, and understand different kinds of user-defined functions in C++.