Functions

Functions let you name a block of code and reuse it. Instead of copying the same logic in three places, you write it once as a function and call it wherever you need it.

What you'll learn

• How to define a function with def
• How parameters and return values work
• What scope means (local vs global variables)
• Default argument values

Instructions

1. Write a function celsius_to_fahrenheit(c) that converts Celsius to Fahrenheit.

• Formula: F = C * 9/5 + 32

2. Write a function classify_temp(f) that returns a string:

• Below 32 → "freezing"
• 32–59 → "cold"
• 60–79 → "comfortable"
• 80 and above → "hot"

3. Read a Celsius temperature from stdin. Convert it, classify it, and print both.

Example output for input 22:

22°C = 71.6°F
Classification: comfortable

Key concepts

Defining a function:

def greet(name):
    return f"Hello, {name}!"

• def starts the definition
• name is a parameter — a placeholder for the value you'll pass in
• return sends a value back to the caller

Calling a function:

message = greet("Alice")  # "Hello, Alice!"

Default arguments let you make parameters optional:

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

Scope: Variables created inside a function only exist inside that function. They don't leak out.

Hints

• Use round() if you want to limit decimal places: round(71.6, 1).
• Your classify_temp function should use if/elif/else — you already know how from the conditionals lesson.
• Make sure you're calling the function and printing the result, not just defining it.