While Loops - Persistent Patterns

Card 9 of 15

Why Do We Need Loops?

"Problem: Repeating actions require you to copy and paste the same line multiple times.
Solution: We can repeat something using a structure called a loop."

The Problem of Repetition

# Without loops - tedious and error-prone
print("Hello")
print("Hello")
print("Hello")
print("Hello")
print("Hello")

# What if we need 100 times? 1000 times?

While Loop: The Repeating If Statement

WHILE condition is True:
Keep executing this block

↻

Think: "Keep doing this AS LONG AS the condition is true"

Key Insight: While loop checks the condition BEFORE each repetition. If condition becomes False, loop stops.

Interactive While Loop

Count up to:

Click 'Run' or 'Step Through' to begin

Output will appear here...

The Anatomy of a While Loop

counter = 0           # 1. Initialize variable
while counter < 5:    # 2. Check condition
    print(counter)    # 3. Execute code block
    counter += 1      # 4. Update variable (crucial!)

# Output: 0, 1, 2, 3, 4

Critical Pitfall: Forgetting to update the variable leads to an infinite loop - the program never stops!

When to Use While Loops

"While loops are best for repeating an indefinite number of times - when you don't know how long it's going to take."

# Good use case: Keep asking until valid input
password = ""
while password != "secret":
    password = input("Enter password: ")
print("Access granted!")

# Another good use: Game loop
game_running = True
while game_running:
    play_turn()
    if player_won():
        game_running = False

Mental Model: A while loop is like a security guard checking your ID. As long as the condition is True, they let you pass through again. Once it's False, the loop stops.

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