What's wrong with my prime number function?

Question

https://code.sololearn.com/c39ut0Ji18An/?ref=app

Answer 1

Baran Aldemir, you wrote:

if number is divisible
not prime
else
prime

This means that the first number that is no divisor will already say it's a prime and end the search.

But you have to check if there is *not any* divisor, only then you'll know it's prime.

Say, the number 14.

Divisible by 3 will be False. So: prime.

But 14 is divisible by 7 - it's no prime! But you stop checking already at 3.

That's why have to wait till after the loop.

Answer 2

This is a corrected version of your function.

def is_it_prime(number):
if(number <= 1):
print ("{} is not a prime number".format(number))
# After you got a result
# you need to abort the function
return
elif(number == 2):
print ("{} is a prime number".format(number))
# same here
return
else:
for i in range(2,number):
if (number % i == 0):
print ("{} is not a prime number".format(number))
return # instead of break
# This was in the loop before
# But only after all numbers
# have been checked, you can
# know if it's prime
print ("{} is a prime number".format(number))

Answer 3

HonFu
You said
#But only after all numbers have
#been checked, you can
# know if it's a prime

Why is that?

If I find any number (except for 1 and my main number itself) divides my main number without remainder, it means my main number is not a prime number. Otherwise it should be a prime number.

Is my logic wrong?

Answer 4

HonFu Okay okay you meant the loop. Got it. Thanks a lot.👍