Chapter 16: While Loops

🚀 Open Notebook

📺 Video Tutorial

While loops in Python are easy! ♾️ (8:04)

📚 What You’ll Learn

Execute code repeatedly while a condition is true - essential for creating interactive programs!

🎯 Learning Objectives

• Understand while loop syntax

• Create loops with conditions

• Use while loops for user input validation

• Avoid infinite loops

• Use break and continue statements

📖 Concept Explanation

What is a While Loop?

A while loop repeatedly executes code as long as a condition remains True.

Syntax

while condition:
    # code to execute
    # update condition eventually!

How It Works

1. Check if condition is True

2. If True, execute the code block

3. Go back to step 1

4. If False, exit the loop

💡 Examples

Example 1: Age Verification

age = int(input("Enter your age: "))

while age < 18:
    print("You are a minor")
    age = int(input("Enter your age: "))

print("You are an adult!")

Example 2: Countdown

count = 5
while count > 0:
    print(count)
    count -= 1
print("Blastoff!")

Example 3: Sum Numbers Until Zero

total = 0
number = int(input("Enter a number (0 to stop): "))

while number != 0:
    total += number
    number = int(input("Enter a number (0 to stop): "))

print(f"Total: {total}")

Example 4: Password Validator

password = input("Enter password: ")

while len(password) < 8:
    print("Password must be at least 8 characters!")
    password = input("Enter password: ")

print("Password accepted!")

✍️ Practice Exercises

1. Create a number guessing game

2. Keep asking for positive numbers until user enters negative

3. Validate email format (must contain @)

4. Create a simple menu system

5. Build a countdown timer

6. Make a multiplication drill program

📝 Loop Control Statements

break - Exit Loop Early

count = 0
while True:  # Infinite loop
    count += 1
    if count > 5:
        break  # Exit loop
    print(count)
# Prints: 1, 2, 3, 4, 5

continue - Skip Current Iteration

count = 0
while count < 10:
    count += 1
    if count % 2 == 0:
        continue  # Skip even numbers
    print(count)
# Prints: 1, 3, 5, 7, 9

🔍 Common Mistakes

Infinite Loops

# Wrong: Condition never becomes False
count = 1
while count > 0:
    print(count)  # Runs forever!

# Correct: Update condition
count = 5
while count > 0:
    print(count)
    count -= 1  # Eventually becomes 0

🎮 Real-World Examples

ATM Machine

balance = 1000

while True:
    print("\n1. Check Balance")
    print("2. Withdraw")
    print("3. Exit")
    
    choice = input("Choose: ")
    
    if choice == "1":
        print(f"Balance: ${balance}")
    elif choice == "2":
        amount = float(input("Amount: "))
        if amount <= balance:
            balance -= amount
            print(f"Withdrawn: ${amount}")
        else:
            print("Insufficient funds")
    elif choice == "3":
        break
    else:
        print("Invalid choice")

🚀 Challenge Projects

1. Login System: 3 attempts before lockout

2. Shopping Cart: Add items until user is done

3. Grade Calculator: Keep accepting scores until user enters “done”

4. Dice Game: Roll until you get 6

5. Calculator Loop: Perform calculations until user quits

🎓 Key Takeaways from Video

1. Strings are text data enclosed in quotes

2. Use loops to repeat actions

3. Use if-elif-else for conditional logic

💡 These points cover the main concepts from the video tutorial to help reinforce your learning.

🔗 Next Chapter

Continue to Chapter 17: Interest Calculator to build a compound interest calculator!