Function vs. Procedure — What's the Difference?

A function in programming is a segment of code that takes input, processes it, and returns a value. Functions are integral to functional programming and are used to encapsulate code that performs a specific computation. On the other hand, a procedure, often referred to as a subroutine, is similar but typically does not return a value. Instead, procedures execute a series of operations, often affecting the program's state or performing an action.

While functions are used to calculate and return values, making them highly useful for mathematical computations and processing data, procedures are used to execute tasks such as modifying global variables, handling files, or generating outputs. This distinction highlights their different roles in programming paradigms.

In terms of usage, functions are often employed when a return value is necessary for further computations or conditions within a program. Whereas procedures are utilized when a task needs to be performed, such as updating a database or writing to a file, where a return value might not be needed.

From a syntax perspective, most programming languages differentiate between functions and procedures by the presence of a return statement. Functions will typically use return statements to send a result back to the caller, while procedures might complete without such a statement.

In practical application, a developer might choose a function over a procedure when they need to maintain immutability and statelessness in their code, which is particularly common in functional programming. Conversely, procedures are often chosen in procedural programming contexts where operations rather than outputs are the focus.