+ 2

# Nested Loops

Can you please explain this code for me? Thanks. for i in range(1,10): is_prime = True for k in range(2,i): if (i%k) == 0: print(i, " is divisable by", k) is_prime = False if is_prime: print(i, " is prime ")

5th Sep 2018, 3:24 AM
Felix 0
Felix bro it's better to see on YouTube for better understanding while it's hard to understand in comments.... don't worry u will get it ..👍😎
6th Sep 2018, 5:43 PM
+ 4
In the second loop is statement that check which number from the first loop( "possibles prime numbers") is divisible by any number from range from 2 to number. If the number is divisible by any number in this range the statement marks the number as non-prime number(is_prime= False). Else it prints the number.
5th Sep 2018, 6:13 AM
patos + 3
Felix Do u know what is the prime number? If u know try to think about this code. If u will have trouble with it I can explain.
5th Sep 2018, 4:18 AM
patos + 3
outer for loop: test for numbers 1-10 if they are prime or not By default say it is a prime. inner loop: test if the number is divisible by any number between 2 and itself (excluded) That is done with the modulus operator % which tells you the rest/remainder of a division. So e.g. for 5 it goes like this: 5%2 = 1 --> not divisble by 2 5%3 = 2 --> not divisible by 3 5%4 = 1 --> not divisible by 4 So the if-condition is always wrong and is_prime will stay true. For the number 4 however, you get: 4%2 = 0 --> divisable by 2 You enter the if-branch and is_prime is set to false. 4%3 = 1 --> not divisable by 3 You see, even if you already know that it is not a prime, the loop continous. So for just detecting primes it is quite in-effecient for larger numbers. Also to show every number for which it is divisable it is not as efficient, since for e.g. 8 you know that if it is divisable by 2, it is also divisable by 4. More sophisticated methods exist, but this a nice start to get familiar with it :)
5th Sep 2018, 6:07 AM
Matthias + 1
Yes, I know what prime number is but I'm having trouble to understand the codes. Can you please help me understand? Thanks.
5th Sep 2018, 5:51 AM
Felix 0
I got this already. I do understand the codes now from range() to indentation. Thanks for your reply.
7th Sep 2018, 11:57 PM
Felix 0
you know C language?? example : In C language, for(initialisation,condition,inc/dec operation) { statements; } In python language, for i in range(initialisation starts with given number here , limits upto n number and use every time less than conditions here, how many numbers increment/decrement ): example : '''for(i=1;i<n;i++) -> in c language ''' //i++ -> i=i+1...i.e increment by 1 for i in range(1,n,1):
14th Sep 2018, 3:11 AM
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