Day 6 of 30: 🔀 Conditional Logic

Learn how to make decisions in your code using if, elif, and else!

May 06, 2025

🔄 Quick Recap (Day 5)

You mastered writing clean code with proper naming and formatting.
You learned to spot and fix simple syntax errors.

🎯 What You’ll Learn Today

How to use if statements to run code only when a condition is true.
How to chain conditions with elif.
How to provide a fallback with else.
Understanding truthy and falsy values in Python.

📖 Overview: Making Decisions with `if`

In everyday life, you make choices: “If it’s raining, I take an umbrella.” Code can do the same:

if is_raining:
    print("Take an umbrella!")

if checks the condition inside parentheses (or after if).
If the condition is True, the indented block runs.

Chaining with `elif` and `else`

Sometimes there are multiple options:

temperature = 15
if temperature > 25:
    print("It's hot, wear shorts!")
elif temperature >= 15:
    print("Nice weather, wear something comfortable.")
else:
    print("It's cold, bundle up!")

elif stands for “else if.” It checks only if all previous if or elif conditions were False.
else runs when none of the above conditions are True.

Truthy and Falsy Values

Python considers certain values as False in conditions:

False, 0, 0.0, '' (empty string), [] (empty list), {} (empty dict), None
All others are True. You can write:

items = []
if items:
    print("We have items!")
else:
    print("No items found.")

Since items is empty ([]), it’s falsy, so the else block runs.

🧙‍♂️ Take the Wand and Try Yourself

Create a file named check_number.py.
Write code that:
- Prompts the user to enter a number (use input()).
- Converts the input to an integer.
- Uses if / elif / else to print:
  - “Positive” if the number is greater than 0.
  - “Zero” if it equals 0.
  - “Negative” if it is less than 0.
Run your script and test with different numbers.

Solution Example (check_number.py):

# check_number.py
num = int(input("Enter a number: "))

if num > 0:
    print("Positive")
elif num == 0:
    print("Zero")
else:
    print("Negative")

Expected interaction:

Enter a number: 5
Positive

Enter a number: 0
Zero

Enter a number: -3
Negative

Run:

python check_number.py

Great work! Conditional logic opens up many possibilities.
Next up: Day 7: Looping Constructs, where you’ll learn how to repeat tasks automatically.

Day 6 of 30: 🔀 Conditional Logic

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