while-loops.md

Python by Example: While Loops

A while loop repeats as long as a condition is true. Use it when you don't know in advance how many iterations you need—for example, reading input until the user quits or retrying until success. Be careful: if the condition never becomes false, you get an infinite loop.

What you'll learn:

• The while loop syntax
• Updating the loop variable to avoid infinite loops
• Using break to exit early

count = 0
while count < 3:
    print(count)
    count += 1

# Break out of a loop
n = 0
while True:
    print(n)
    n += 1
    if n >= 3:
        break

The first loop runs while count < 3; count += 1 ensures we eventually stop. The second uses while True with break—a common pattern when the exit condition is complex.

To run this program:

$ python source/while-loops.py
0
1
2
0
1
2

Tip: Always ensure your condition can become false, or that break will run. Otherwise the loop runs forever. Press Ctrl+C to stop an infinite loop.

Try it: Change the condition to count < 5 and see how the output changes.

Source: while-loops.py

Next: If/Else