Repeating with while

In Phase I you used for loops to repeat a fixed number of times. But sometimes you don’t know how many times — you want to keep going until something happens. “Keep asking until the player guesses right.” “Keep going until the countdown hits zero.” That’s a while loop.

while: repeat as long as it’s true

A while loop checks a yes/no test, and repeats its indented lines as long as the test is True:

while some_test:
    # repeat while the test stays true

Here’s a countdown. Each time around, n gets one smaller, until it’s no longer greater than 0:

 
  

The key is that something inside the loop changes the test (n = n - 1). Without that, the test would stay True forever and the loop would never stop!


Try it 🎯


    

  1. Change n = 5 to n = 10.
    2. 

  2. Count up instead: start n = 1, loop while n <= 5, print n, then n = n + 1.
    3. 



A real game: guess the number


This is the classic. The computer picks a secret number, and the loop keeps asking until you guess it — giving “higher” or “lower” hints along the way:


   
   
 
 
  

Look at how it works: the loop runs while your guess isn’t the secret. Each wrong guess triggers a hint, and the box pops up again. The moment guess == secret, the test becomes False and the loop ends. Play a few rounds!


Predict it 🔮


How many numbers does this print? Trace it before running:


   
   
 
 
  

(Three lines: loop 3, loop 2, loop 1. When n reaches 0 the test n > 0 is False, so it stops.)


Fix the bug 🐞


This countdown is supposed to print 5 down to 1, but it prints an extra 0 at the end. Look at the test:


   
   
 
 
  

(n >= 0 keeps going while n is 0 too. To stop at 1, use while n > 0:.)




⚠️ One rule with while: make sure something inside the loop moves it toward stopping (like n = n - 1). If nothing changes, the loop runs forever!




Your mission 🚀


Make a “password gate”: keep asking for the password until the user types "open". Use a while loop that repeats while the answer is not "open":


   
   
 
 
  

Run it, type some wrong words, then type open. Then try changing the magic word to your own secret.


What you learned today


    

  • A while loop repeats as long as its test is True.
    • 

  • Something inside the loop must move it toward stopping.
    • 

  • while is perfect when you don’t know the number of repeats ahead of time — like guessing games and “keep asking until…”.
    • 



Next time we tackle lists — a way to hold many things at once, like a whole list of scores or names. It’s the door to working with data. 📋
   
 
 
 
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