Why this While loop is not breaking or stopping
I have added some output screenshot
term = 0
i = 13
while True:
print i > 1
print "i = ",i
if i == 1:
term += 1
break
if i%2 == 0:
i = i / 2
term += 1
if i%2 != 0:
i = i * 3 + 1
term += 1
I also tried This way too
term = 1
i = 13
while i > 1:
print i > 1
if i%2 == 0:
i = i / 2
term += 1
if i%2 != 0:
i = i * 3 + 1
term += 1
Use elif to make the cases mutually exclusive. You don't want multiple if statements to execute in the same loop iteration.
if i%2 == 0:
i = i / 2
term += 1
elif i%2 != 0:
i = i * 3 + 1
term += 1
Or just make it else since the second condition is redundant.
if i%2 == 0:
i = i / 2
term += 1
else:
i = i * 3 + 1
term += 1
The reason it oscillates between 2 and 4 as written is because 2 causes both if statements to run. 2 is even so the first one runs and halves i, making it 1. Now it's odd and the second one triggers, turning 1 into 4.
if i%2 == 0:
i = i / 2 # 2 --> 1
term += 1
if i%2 != 0:
i = i * 3 + 1 # 1 --> 4
term += 1
The next iteration 4 becomes 2.
if i%2 == 0:
i = i / 2 # 4 --> 2
term += 1
These two iterations repeat over and over in an endless cycle.
Let's say your i is 2. It is divisible by 2, so if i % 2 == 0 fires, and i becomes 1. And the code continues to execute, so now we are at if i % 2 != 0 line, and this condition is also true, because you just modified i and it's now 1. So i becomes 4.
Your modified second attempt, which prevents the second condition from being checked if the first one succeeds, is below:
term = 1
i = 13
while i > 1:
print(i > 1)
if i % 2 == 0:
i = i / 2
term += 1
elif i % 2 != 0:
i = i * 3 + 1
term += 1
Also notice that you actually don't need to check the second condition, as it is definitely true if the first one is not, so elif ... line can be replaced just with else:
You can also use continue keyword to stop the rest of the loop from executing if the first condition is true:
term = 1
i = 13
while i > 1:
print(i > 1)
if i % 2 == 0:
i = i / 2
term += 1
continue
if i % 2 != 0:
i = i * 3 + 1
term += 1
Your first attempt has exactly the same problem; fixing it I leave as an exercise for the reader :)
P.S. do not learn Python 2
The problem is:
if i%2 == 0:
i = i / 2
term += 1
if i%2 != 0:
i = i * 3 + 1
term += 1
The problem is that, if i % 2 == 0 is true, it will remain true until i = 1. Once i = 1, i % 2 != 0 executes and makes i = 4.
ioscillates between 2 and 4 infinitely based on how you've encoded the math for the nextiso the stopping condition is unreachable. What is it supposed to do? Is this supposed to run Collatz?breakstatement in the first one, and the second has a loop condition.printstatement). As a beginner, you should be learning Python 3 instead.