2.7 Functions and Procedures

Characteristics:

• May take parameters
• Must return a value

Purpose: To perform a task and return a result.

When used: When a value needs to be calculated or reused.

Python example:

def calculate_total(price, quantity):
    return price * quantity

total = calculate_total(5, 4)
print(total)
        

Characteristics:

• May take parameters
• Must not return a value

Purpose: To carry out an action.

When used: When performing a task such as displaying output.

Python note: In Python, procedures are functions that return no value.

Python example:

def greet(name):
    print("Hello", name)

greet("Alex")
        

Functions and procedures can come from:

• User‑written – created by the programmer
• Built‑in – provided by the language (e.g. print, len)
• Standard libraries – included with the language
• Third‑party libraries – supplied externally

Python example (built‑in):

numbers = [1, 2, 3]
print(len(numbers))
        

Python example (library):

import math
print(math.sqrt(16))
        

Benefits:

• Saves development time
• Often tested and reliable
• Improves code readability

Drawbacks:

• Less control over implementation
• May include unnecessary features
• Dependency on external updates

Example:

def add(a, b):
    return a + b

result = add(3, 4)
print(result)
        

This function takes two values, adds them, and outputs the result.

Python example:

def is_even(number):
    return number % 2 == 0

num = 6
if is_even(num):
    print("Even")
else:
    print("Odd")
        

Incorrect code:

def multiply(a, b):
print(a * b)

multiply(2, 3)
        

Problems:

• Indentation error in function body

Corrected code:

def multiply(a, b):
    print(a * b)

multiply(2, 3)