*What is a Function?*

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

Think of it as a machine: you give it some input (arguments), it processes something, and then gives you output.


✅ *Defining a Function*

Here’s the basic structure:

def greet():
print(Hello, Python learner!)

To call or run the function:

greet()

*Output:*

Hello, Python learner!


✅ *Function with Parameters*

You can make your function accept values using parameters:

def greet(name):
print(fHello, name!)

greet(Sam)

*Output:*

Hello, Sam!


✅ *Return Values*

Functions can return values instead of just printing them:

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

result = add(3, 5)
print(result)

*Output:* 8


*Mini Project: Prime Number Checker*

Let’s use what we learned to create a small, useful function!

def is_prime(n):
if n 2:
return False
for i in range(2, int(n**0.5)+1):
if n % i == 0:
return False
return True

Try it!
num = int(input(Enter a number: ))
if is_prime(num):
print(It's a prime number.)
else:
print(Not a prime number.)

*This project introduces:*

- Logic inside a function

- Conditional checks

- Looping through a range