Sum All Primes Intermediate Algorithm Scripting Free Code Camp

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[winiswamtshingwana]

You are God sent since I started following you my life has changed for the better keep up the good work you are a blessing to us here

[jacklyons]

I did a little console logging to make this all a bit clearer -- here were my results which show what is divisible (and therefore not a prime number)

"this is i: 2"
"and this is j: 2"
2 is prime
"this is i: 3"
"and this is j: 2"
"and this is j: 3"
3 is prime
"this is i: 4"
"and this is j: 2" * break
"this is i: 5"
"and this is j: 2"
"and this is j: 3"
"and this is j: 4"
"and this is j: 5"
5 is prime
"this is i: 6"
"and this is j: 2" * break
"this is i: 7"
"and this is j: 2"
"and this is j: 3"
"and this is j: 4"
"and this is j: 5"
"and this is j: 6"
"and this is j: 7"
7 is prime
"this is i: 8"
"and this is j: 2" * break
"this is i: 9"
"and this is j: 2"
"and this is j: 3" * break

[danutzz]

cool, best explanation i've managed to find out there ;)

[BLloyd]

Your explanation really helped me tremendously especially how array.reduce works. Thank you very much. I went over your way about five times to make sure I really got it into my head.

[ShelJones]

Good walkthrough. I really needed help figuring out identifying the primes. I needed to work it out on paper before I completely understood the nested for loops. A few attempts crashed my browser.

[christianrodier]

that makes it much easier to understand. thanks

[murghay]

Certainly a good piece of coding. Thought it just got a little confusing. I think creating an isPrime function and then throwing that in an if-condition in the main function for loop really makes it seem a little easier. Just that moment where you felt you needed a second to explain seemed as if abstracting the "isPrime" would be easier to go with. Sorry if this is coming off as aggressively critical. Love all the help you give.

[kimonushki]

I struggled on this challenge, after a while came up with this (not ideal for high values but passes this test just fine):

function sumPrimes(num) {

// test for primacy

function primacy(test){
for (var i = 2 ; i < test ; i++){
if (test % i === 0){
return false;
}
}
return true;
}

var arr = [2];

// iterate from 3 until num (and test)

for (var prime = 3 ; prime <= num ; prime += 2){
if (primacy(prime) === true) {
arr.push(prime);
}
}

// add the array together

var answer = arr.reduce(function(a, b){
return a + b;
});

return answer;

}

[CashBarnes]

I didn't want to use reduce either. I just added each prime iteration to var sum = 0 in the first if statement.
if (i===j){
sum = sum+i;
}
if (i%j===0){
break;
}

[DupaCycDupa]

Is it bad or unspeakable to use for loop for adding? Becouse that's how I did it.

[chriscullen]

Good stuff.. I did it a different way but Im wondering how your break line works.
Wouldnt it break on the first non prime number?

[sahil]

what if i is 4 and j is also 4... both the conditions are met then why isnt 4 been pushed to the array

[arletbode]

I can't figure out why the for loops work :/

[davidobaro]

Amazing explanation. I just don't really get the logic behind: (i===j)