*What is Recursion?*

Recursion is when a function calls itself to solve smaller parts of a problem — ideal for tasks that can be broken down into repetitive subproblems.

✅ *Basic Recursive Structure*

def function_name():
base condition
if condition:
return something
else:
return function_name() recursive call

Without a base condition, the function will keep calling itself forever — causing a RecursionError.

*Example 1: Factorial Using Recursion*

def factorial(n):
if n == 0 or n == 1: base case
return 1
else:
return n * factorial(n - 1)

print(factorial(5)) Output: 120

*Here’s how it works:*

factorial(5)
→ 5 * factorial(4)
→ 5 * 4 * factorial(3)
→ 5 * 4 * 3 * factorial(2)
→ ...
→ 5 * 4 * 3 * 2 * 1 = 120


*Example 2: Fibonacci Series Using Recursion*

def fibonacci(n):
if n == 0:
return 0
elif n == 1:
return 1
else:
return fibonacci(n-1) + fibonacci(n-2)

for i in range(7):
print(fibonacci(i), end=' ') Output: 0 1 1 2 3 5 8


*Mini Project:*

*Factorial & Fibonacci Calculator*

def factorial(n):
return 1 if n = 1 else n * factorial(n - 1)

def fibonacci(n):
if n = 1:
return n
else:
return fibonacci(n - 1) + fibonacci(n - 2)

num = int(input(Enter a number: ))
print(Factorial:, factorial(num))
print(Fibonacci:, fibonacci(num))


This covers:

- Recursive thinking
- Base vs. recursive case
- Classic math problems