Subroutines: Functions and Procedures

A subroutine is a named block of code that performs a specific task. Subroutines make programs easier to read, test, debug, and maintain. They are a crucial part of GCSE Computer Science (AQA 3.2 / OCR J277 2.2).

---

What Is a Subroutine?

A subroutine is a self-contained section of code that can be called (invoked) by name whenever it is needed. Instead of writing the same code multiple times, you write it once as a subroutine and call it whenever required.

There are two types of subroutine:

Type	Description	Returns a value?
Procedure	Performs a task but does NOT return a value	No
Function	Performs a task and RETURNS a value	Yes

Exam Tip: The key distinction is that a function returns a value that can be stored in a variable or used in an expression. A procedure simply carries out an action.

---

Procedures

A procedure performs an action without returning a value.

Pseudocode

SUBROUTINE greet(name)
    OUTPUT "Hello, " + name + "!"
ENDSUBROUTINE

greet("Alice")
greet("Bob")

Python