while Loops, break, continue

while Loops, break, continue

The for loop repeats over a collection. The while loop repeats over a condition — “keep going until…” — which makes it the tool for user input, games, and anything with an unknown number of repetitions.

The basic while

count = 3

while count > 0:
    print(count)
    count -= 1

print("Lift off! 🚀")

Output:

3
2
1
Lift off! 🚀

Read it: “while count is above zero, print it and decrease.” The loop checks the condition before each pass; the moment it’s False, execution jumps past the loop.

The infinite loop — and how to escape it

while True:
    print("This never ends")

while True runs forever… unless something inside breaks out. That’s what break is for:

while True:
    command = input("Type 'quit' to exit: ")
    if command == "quit":
        break                    # exits the loop RIGHT NOW
    print(f"You typed: {command}")

print("Goodbye!")

This shape — while True: + a break condition — is the standard pattern for “keep asking until the user says stop.” The loop condition is deliberately always-true; the break decides when to leave.

The password gate (classic use)

attempts = 3

while attempts > 0:
    password = input("Password: ")
    if password == "open123":
        print("Access granted")
        break
    attempts -= 1
    print(f"Wrong! {attempts} attempt(s) left")
else:
    print("Account locked")

Yes — while can take an else! It runs only when the loop finishes normally (condition became False), not when broken out. Rare but perfect here.

continue — skip this one, keep looping

break exits the loop entirely; continue skips just the current pass:

for number in range(1, 11):
    if number % 2 == 0:
        continue               # skip evens
    print(number)              # odds only: 1 3 5 7 9

Real use — process only valid lines:

for line in lines:
    if line == "":             # skip empty lines
        continue
    process(line)

break vs continue — one screen

The #1 while bug: forgetting to change the condition

count = 3
while count > 0:
    print(count)
    # count -= 1 is MISSING — infinite loop!

This program never ends — count stays 3 forever. If your terminal freezes in a print storm: Ctrl+C kills the program. Every programmer has done this; now you know the escape hatch before you need it.

The mental checklist for every while loop:

1. Initialize — what does the condition check? (count = 3)
2. Change — what moves it toward False? (count -= 1)
3. Escape — is there a break for special cases?

Common Errors & Fixes

• Infinite loop / frozen terminal — condition never becomes False. Ctrl+C, then find the missing update line.
• Loop runs one extra time — you update the variable after using it; reorder.
• while count = 3: — assignment in a condition; use == (or better, a real condition).

✅ Checkpoint

1. for vs while — what decides which to use? (Known collection/count → for; unknown repetitions until a condition → while)
2. What does break do inside nested loops? (Exits only the innermost loop)
3. When does a while-else run? (Only when the loop ends normally — not via break)
4. Your terminal is frozen printing — what do you press? (Ctrl+C)

Next: looping like a professional — enumerate, items, and the patterns that make loops clean.