The while Loop

The while Loop

A while loop repeats its block as long as a condition is True. Use it when you do not know in advance how many times to repeat.

n = 1234
digits = 0
while n > 0:
    n = n // 10      # remove the last digit
    digits += 1
print(digits)        # 4

Something inside the loop must change the condition, here n gets smaller each time. If nothing changes it, the condition stays True forever and the program never stops: an infinite loop.

Two tricks with // and % are used again and again with whole numbers: n % 10 is the last digit of n, and n // 10 is n without its last digit.

n = int(input())
total = 0
while n > 0:
    # add the last digit to total, then remove it from n
    n = 0
print(total)