View source for 3.4.1 Definition and Purpose

=== 3.4.1 Definition and Purpose ===
A '''function''' (or method) is a named section of a program that performs a specific, well-defined task.

'''Definition:'''

* A function is a '''self-contained block of code''' designed to do a particular job.
* It has a '''name''' (like <code>calculateArea</code> or <code>displayMessage</code>).
* It can take '''inputs''' (called parameters or arguments).
* It can produce an '''output''' (called a return value).

'''Purpose:''' Functions are super important in programming for several reasons:

# '''Reusability:'''
#* Instead of writing the same lines of code multiple times, you write them once inside a function. Then, you can "call" or "use" that function whenever you need that task performed.
#* '''Example:''' If you need to calculate the area of many different rectangles throughout your program, you write an <code>calculateArea()</code> function once, and then just call <code>calculateArea()</code> whenever you need it.
# '''Organization and Readability:'''
#* Functions break down a large, complex program into smaller, more manageable pieces. This makes your code much easier to read, understand, and debug.
#* Imagine reading a book that's just one giant paragraph versus a book with chapters and sections. Functions are like chapters!
# '''Modularity (Breaking into Modules):'''
#* Each function can be thought of as a separate module or component. If something goes wrong, you often only need to look at the function that's responsible for that specific task, rather than searching through the entire program.
#* This also makes it easier for multiple programmers to work on different parts of the same big program without interfering with each other too much.
# '''Abstraction:'''
#* When you call a function like <code>print("Hello")</code>, you don't need to know ''how'' the computer actually makes the letters appear on the screen. You just need to know that <code>print()</code> will display text. Functions hide the complex details, allowing you to focus on the bigger picture.

In short, functions are like the building blocks of well-structured programs.

'''Bibliography:'''

* '''GeeksforGeeks - Functions in C++''': https://www.geeksforgeeks.org/functions-in-c/ (Concepts apply broadly)
* '''W3Schools - Python Functions''': https://www.w3schools.com/python/python_functions.asp
* '''Wikipedia - Subroutine''': https://en.wikipedia.org/wiki/Subroutine