Controlling Loops with break and continue

Why this matters

Sometimes you do not know in advance when a loop should end (keep asking until the user types “quit”), or you want to skip certain items. break and continue give you precise control.

The idea

• break ends the loop immediately.
• continue skips the rest of this pass and jumps to the next one.

for number in range(1, 8):
    if number == 3:
        continue          # skip 3
    if number == 6:
        break             # stop completely at 6
    print(number)         # prints 1, 2, 4, 5

A very common pattern pairs while True: (a loop that never ends on its own) with break when a special sentinel value shows up:

while True:
    word = input("Type a word (or 'quit'): ")
    if word == "quit":
        break
    print("You typed", word)
print("Goodbye")

This is often clearer than trying to squeeze the “stop” rule into the loop condition, especially when you need to read the input before you can decide.

Because while True never ends by itself, make sure there is always a path to break.

Try it

Write a loop that prints the numbers 1 to 20, but skips multiples of 3 and stops completely when it reaches 15. (Hint: number % 3 == 0 tests for a multiple of 3.)

Your turn

Write a program that adds up numbers typed by the user:

• Keep asking with input("Number: ").
• When the user types 0, stop asking.
• Negative numbers are ignored: they are not added and not counted.
• At the end, print the sum, and how many numbers were added.

If the user types 5, 3, 0, the output is:

Sum: 8
Counted: 2

Recap

• break leaves the loop; continue skips to the next pass.
• while True: plus break is the standard “keep going until I say stop” loop.
• A sentinel value (like 0 or "quit") tells the program the input is finished.

Common mistakes

• Putting the sentinel check after using the value: check for 0 first, before you add it.
• Using continue before updating a counter in a while loop. The condition never changes and the loop sticks.
• No way out of while True. If you forget the break, press Stop ■.