When Should You Use a While Loop?

Use a while loop when you do not know in advance how many iterations are needed. For example, reading user input until they type "quit", or running a game until the player loses. If you already know the count, a for loop is cleaner.

Basic Syntax

count = 0
while count < 5:
    print(count)
    count += 1

The loop body runs while the condition is True. Forgetting to update count creates an infinite loop — the #1 beginner bug.

Breaking Out Early

while True:
    answer = input("Type 'quit' to exit: ")
    if answer == "quit":
        break
    print(f"You said: {answer}")

Skipping Iterations with continue

n = 0
while n < 10:
    n += 1
    if n % 2 == 0:
        continue
    print(n)  # prints odd numbers only

While vs For: Choosing the Right Loop

Common HKDSE Pattern: Input Validation

age = -1
while age < 0 or age > 120:
    age = int(input("Enter your age: "))
print(f"Age accepted: {age}")
💡 Tip: Always guarantee your loop variable changes inside the body, or structure your loop around a break. That single habit eliminates most infinite-loop bugs.

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