How do I make it so it can loop?

Question

I need to test whether n is a multiple of 2 and then divide the number by 2. If the number isn't a multiple of 2, then I have to do 3*n+2.

How do I make it loop so I can get the following: 12, 6, 3, 10, 5, 16, 8, 4, 2, 1?

Here's my current code:

n=12
while n!=0:
    if n%2==0:
        print (n)
    n=n/2
    if n!=n%2:
        if n !=1:
            n = 3*n+2
    else:
        break
print(n)

`n!=n%2` is not how you check if a number is divisible by 2. You want `n % 2 == 0`. Also this is the Collatz Conjecture. — Random Davis, Sep 12 '22 at 22:59
You want `n=n//2` or `n \\= 2` (integer division)to keep numbers as integers. — DarrylG, Sep 12 '22 at 23:04
@RandomDavis I am trying get one that is divisible by 2 and another one who multiplies, I wrote n!=n%2 because I thought it would give me n when its not divisible by 2. Sorry for the confusion. — Marcelo Zevallos, Sep 12 '22 at 23:11
@MarceloZevallos if the answer helped and fixed your issue, please consider accepting it by clicking the checkmark — Ali, Sep 15 '22 at 09:13

Ramsudharsan Manoharan · Answer 1 · 2022-09-12T23:22:05.517

0

First of all your formula of 3*n + 2 will lead to infinite loop. According your sample output, it needs to be 3*n + 1.

n = 12
while n >= 1:
    print(n, end=' ')

    if n == 1:
        break

    if n % 2 == 0:
        n = n // 2
    else:
        n = 3 * n + 1

edited Sep 12 '22 at 23:22

answered Sep 12 '22 at 23:11

Ramsudharsan Manoharan

635
1
7
18

The inner `if` is never going to be needed. If `n==1`, the while loop will have ended before getting to that part of the code. – Blckknght Sep 12 '22 at 23:16
Missed that edge case. Now its corrected – Ramsudharsan Manoharan Sep 12 '22 at 23:34

Ali · Accepted Answer · 2022-09-12T23:22:04.067

First note is that it is 3*n+1, second one is that you have to write n=n/2 in your first if.

Overall this code is what you want:

n = 12
while n != 0:
  if n % 2 == 0:
    print(n, end=' ')
    n = n / 2
    
  elif n % 2 != 0:
    if n != 1:
        print(n, end=' ')
        n = 3 * n + 1   
    else:
        print(1)
        break

Or this:

n = 12
while n > 1:
  if n % 2 == 0:
    print(n, end=' ')
    n = n / 2

  elif n % 2 != 0:
    if n != 1:
        print(n, end=' ')
        n = 3 * n + 1   
    else:
        print(1)

Good luck

How do I make it so it can loop?

2 Answers2