Lesson 10: Functions

Topics Covered:

• What is a function?
• Defining and calling functions
• Function parameters (arguments)
• Return values from functions

What is a Function?

A function is a reusable block of code that performs a specific task.

Defining a Function

def greet():
    print("Hello, friend!")

Calling a Function

greet()  # Output: Hello, friend!

Functions with Parameters

Functions can take inputs called parameters:

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

greet("Alice")  # Output: Hello, Alice

Functions with Return Values

Functions can send back a result using return:

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

result = add(3, 4)
print("Sum is", result)  # Output: Sum is 7

Activity: Write a Function

• Create a function square that takes a number and returns its square.
• Call the function with different numbers and print the results.

def square(x):
    return x * x

print(square(5))  # 25
print(square(10)) # 100

Challenge

• Write a function is_even that returns True if a number is even, False otherwise.
• Test it with several numbers.

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

print(is_even(4))  # True
print(is_even(7))  # False