As programs grow, copying the same code in multiple places is a nightmare — change one copy and forget the other and you've introduced a bug.

Subroutines (also called subprograms) solve this: give a block of code a name, and call it whenever you need it.

There are two types:

- Procedure — runs a block of code, does NOT return a value

- Function — runs a block of code and returns a value

```python

# Procedure — just does something

def show_menu():

print("1: Play game")

print("2: High scores")

print("3: Quit")

show_menu() # call it once

# ... later ...

show_menu() # call it again — same code, no duplication

```