My Python while loop is not terminating and I don't know why

Question

It seems like the while loop should terminate once the start int == 1, but it keeps going. It also seems it's not actually printing the values....just 0

Given a positive integer n, the following rules will always create a sequence that ends with 1, called the hailstone sequence:

• If n is even, divide it by 2
• If n is odd, multiply it by 3 and add 1(ie 3n +1)
• Continue until n is 1

Write a program that reads an integer as input and prints the hailstone sequence starting with the integer entered. Format the output so that ten integers, each separated by a tab character (\t), are printed per line.

The output format can be achieved as follows: print(n, end='\t')

Ex: If the input is:

25

the output is:

25   76   38   19   58   29   88   44   22   11 
34   17   52   26   13   40   20   10   5    16 
8    4    2    1

My code:

''' Type your code here. '''
start = int()

while True:
    print(start, end='\t')
    if start % 2 == 0:
        start = start/2
        print(start, end='\t')
    elif start % 2 == 1:
        start = (start *3)+1
        print(start, end='\t')
    if start == 1:
        print(start, end='\t')
        break

print(start, end='\t')

Program errors displayed here

Program generated too much output.
Output restricted to 50000 characters.

Check program for any unterminated loops generating output.

Program output displayed here

0   0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.

Answer 1

Your loop isn't terminating because you used 0 as an input and as 0 % 2 == 0 is true and 0/2=0 you become stuck in an infinite loop. you could fix this by raising an exception if start is <=0 like this:

start = int(input())
if start <=0:
    raise Exception('Start must be strictly positive')
while True:
    print(start, end='\t')
    if not start % 2:
        start //= 2
    elif start % 2:
        start = 3*start+1
    if start == 1:
        break