while Loops: Repeat Until It Changes

A while loop repeats its block as long as a condition stays true. Before each pass, Python checks the condition. When it becomes false, the loop stops and the program moves on.

The single most important rule: something inside the loop must eventually make the condition false, or it runs forever. We call that the termination. Watch the counter climb until it fails the test:

count = 1
while count <= 3:
    print(count)
    count = count + 1   # this is what ends the loop
print("done")

That prints 1, 2, 3, then done. Trace it: when count reaches 4, 4 <= 3 is false, so the loop ends. Forgetting the count = count + 1 line would loop forever, so always make sure each pass moves you toward the exit.

A common pattern is accumulating a total. Here we add numbers while a counter walks up:

total = 0
n = 1
while n <= 5:
    total = total + n   # total grows: 1, 3, 6, 10, 15
    n = n + 1           # n moves toward the exit
print(total)            # 15

Read it as: start at the top, do the work, take one step toward stopping, repeat. The counter n both does the work and guarantees the loop ends.