Subroutines (Computer programs)

In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-formed interface and behavior and can be invoked multiple times. Callable units provide a powerful programming tool. The primary purpose is to enable the decomposition of a large and/or complicated problem into chunks that have relatively low cognitive load. These smaller, less complicated chunks (callable units) can become conceptually independent of the larger problem, taking on meaningful names of their own and potentially becoming useful to other unrelated problems through reusability. Judicious application can reduce the cost of developing and maintaining software through modularity and reusability, while increasing quality and reliability. Callable units are present at multiple levels of abstraction in the programming environment. For example, a programmer may write a function in source code that is compiled to machine code that implements similar semantics. There is a callable unit in the source code and an associated one in the machine code, but they are different kinds of callable units—with different implications and features.