Chapter 2: Variables and Numbers 🔢

In Chapter 1, you learned to make Python “speak” using print(). But what if you want Python to remember things? That’s where variables come in — they’re like containers that store information for you.

Variables: Your Data Storage Boxes 📦

Imagine you have a box where you can put things and label it. Whenever you need what’s inside, you just look at the label. That’s exactly what a variable does in Python!

A variable is a name that stores a value. Here’s how you create one:

age = 12
name = "Alex"
favorite_color = "blue"

Let’s break this down:

  • age is the variable name (the label on your box)
  • = is the assignment operator (it means “store this value”)
  • 12 is the value being stored

Variable Naming Rules

You can name variables almost anything, but there are a few rules:

✅ Good variable names:

player_score = 100
first_name = "Jordan"
level_2_complete = True

❌ Invalid variable names:

2nd_place = "Silver"    # Can't start with a number
my-score = 50           # Can't use hyphens
class = "Math"          # Can't use Python keywords

Pro Tips:

  • Use descriptive names: player_health is better than ph
  • Use lowercase with underscores: high_score not highscore or HighScore
  • Make it meaningful: someone reading your code should understand what the variable stores

Using Variables

Once you create a variable, you can use it anywhere in your program:

username = "CodeMaster"
print("Welcome back,")
print(username)

This prints:

Welcome back,
CodeMaster

You can even use variables inside other print statements:

score = 450
print("Your score is:")
print(score)

Updating Variables: Things Change! 🔄

Variables aren’t set in stone — you can change their values whenever you want. That’s why they’re called “variables” (things that vary)!

points = 10
print(points)  # Shows: 10

points = 25
print(points)  # Shows: 25

This is super useful in games. Imagine collecting coins:

coins = 0
print("Starting coins:", coins)

# Player collects 5 coins
coins = 5
print("After level 1:", coins)

# Player collects 3 more coins
coins = 8
print("After level 2:", coins)

A Clever Trick: Updating Based on Current Value

You can update a variable based on its current value:

score = 100
score = score + 50  # Take current score, add 50, store the result
print(score)  # Shows: 150

Think of it like this: “Take what’s in the box, modify it, then put the new value back in the box.”

Python has a shortcut for this:

score = 100
score += 50  # Same as: score = score + 50
print(score)  # Shows: 150

Other shortcuts:

lives = 3
lives -= 1   # Subtract 1 (same as: lives = lives - 1)
print(lives) # Shows: 2

power = 10
power *= 2   # Multiply by 2 (same as: power = power * 2)
print(power) # Shows: 20

Numbers: Integers and Floats 🔢

Python works with two main types of numbers:

1. Integers (Whole Numbers)

Integers are whole numbers without decimal points:

students_in_class = 25
player_level = 7
high_score = 1000
temperature = -5  # Negative numbers work too!

2. Floats (Decimal Numbers)

Floats are numbers with decimal points:

price = 19.99
temperature = 98.6
pi = 3.14159
average_score = 87.5

The name “float” comes from “floating-point number” — a technical term for how computers store decimals.

Why Does It Matter?

Understanding the difference helps you choose the right type:

# Counting things? Use integers
apples = 5

# Measuring things? Use floats
height_in_meters = 1.65

You can check a number’s type:

print(type(42))      # Shows: <class 'int'>
print(type(3.14))    # Shows: <class 'float'>

Math Operations: Python as Your Calculator ➕

Python can do math! Let’s explore the basic operations.

Basic Operations

# Addition
total = 10 + 5
print(total)  # Shows: 15

# Subtraction
difference = 20 - 7
print(difference)  # Shows: 13

# Multiplication
product = 6 * 4
print(product)  # Shows: 24

# Division (always gives a float)
result = 15 / 3
print(result)  # Shows: 5.0

Notice that division always gives you a float, even if the answer is a whole number!

Using Variables in Math

apples = 10
oranges = 15
total_fruit = apples + oranges
print("Total fruit:", total_fruit)  # Shows: Total fruit: 25

You can combine as many operations as you need:

price_per_item = 5
quantity = 3
tax = 2
total_cost = (price_per_item * quantity) + tax
print("Total cost:", total_cost)  # Shows: Total cost: 17

Order of Operations

Python follows the same math rules you learned in school (PEMDAS/BODMAS):

result = 2 + 3 * 4
print(result)  # Shows: 14 (not 20, because multiplication happens first)

result = (2 + 3) * 4
print(result)  # Shows: 20 (parentheses force addition first)

Remember: When in doubt, use parentheses to make your intentions clear!

More Math: Advanced Operations 🎯

Python has a few special math operators that are super handy.

Exponents (Power)

Use ** to raise a number to a power:

squared = 5 ** 2      # 5 to the power of 2
print(squared)        # Shows: 25

cubed = 2 ** 3        # 2 to the power of 3
print(cubed)          # Shows: 8

square_root = 16 ** 0.5  # Square root of 16
print(square_root)    # Shows: 4.0

Floor Division (Integer Division)

Regular division (/) gives you a float. But what if you only want the whole number part? Use //:

result = 17 / 5
print(result)   # Shows: 3.4

result = 17 // 5
print(result)   # Shows: 3 (just the whole number)

Think of it like sharing cookies: if you have 17 cookies and 5 friends, each friend gets 3 whole cookies (with some left over).

Modulus (Remainder)

The % operator gives you the remainder after division:

remainder = 17 % 5
print(remainder)  # Shows: 2

Why? Because 17 divided by 5 is 3 with a remainder of 2.

When is this useful?

  • Checking if a number is even or odd
  • Wrapping numbers around (like in a circular game board)
  • Distributing items evenly
# Check if a number is even
number = 8
if number % 2 == 0:
    print("Even!")  # This runs because 8 % 2 = 0

Quick Recap 🎯

Fantastic work! You’ve learned a lot in this chapter:

✅ Variables store data with meaningful names
✅ Variables can be updated as your program runs
✅ Integers are whole numbers, floats have decimals
✅ Math operations: +, -, *, /
✅ Advanced operations: ** (power), // (floor division), % (remainder)

You now have the tools to make Python remember things and do calculations!

🚀 Hands-On Exercise: Build a Score Calculator

Time to practice! Create a program that simulates a simple game scoring system.

Your Mission:

  1. Create a variable called player_name and store your name in it
  2. Create a variable base_score and set it to 100
  3. The player completes a challenge and earns 50 bonus points — update the score
  4. The player uses a power-up that doubles the score — update it again
  5. The player loses 25 points for a mistake — update once more
  6. Print the player’s name and final score
  7. Bonus: Calculate and print how many complete sets of 100 points the player has (use //)
  8. Extra Bonus: Calculate and print the leftover points after removing complete hundreds (use %)

Example Solution:

# Game Score Calculator

# Player information
player_name = "SkyWalker"
base_score = 100
print("Player:", player_name)
print("Starting score:", base_score)

# Earned bonus points for completing a challenge
base_score += 50
print("After challenge:", base_score)

# Used a power-up to double the score
base_score *= 2
print("After power-up:", base_score)

# Lost points for a mistake
base_score -= 25
print("After mistake:", base_score)

# Final results
print("\n--- Final Results ---")
print("Player:", player_name)
print("Final Score:", base_score)

# Bonus calculations
hundreds = base_score // 100
leftover = base_score % 100
print("Complete hundreds:", hundreds)
print("Leftover points:", leftover)

Challenge Yourself:

  • Add more scoring events (found treasure, defeated enemy, etc.)
  • Calculate an average score if the player played multiple rounds
  • Use exponents to calculate an “achievement multiplier” (like level ** 2)

Remember: Programming is about experimenting. Try different numbers, add your own twists, and see what happens!

What’s Next? 💭

In the next chapter, you’ll learn how to work with text (strings) in more depth — combining words, formatting messages, and making your programs even more interactive!

Keep experimenting, keep learning! You’re building real programming skills.