CODEWITHSUNDEEP
javascriptprimes
user2700923
user2700923

Reputation:

Why does this prime number generator only work on primes up to 7?

http://jsfiddle.net/xCX9W/8/

I noticed this question on Code Review and decided to play with one of the answers' JSfiddles to look at a long list of primes. However, his answer only reached 7. Why?

function findPrimes(lowerLimit, upperLimit) {

    var primes = []; // will become a list of prime numbers

    if (lowerLimit === 2) {
        primes.push(2);
    }

    if (lowerLimit % 2 === 0) {
        lowerLimit++;
    }

    primes_loop: for (var n = lowerLimit; n < upperLimit; n = n + 2) {

        for (var i = 2; i < n; i++) {

            if (n % i === 0) {
                break primes_loop; // n is not prime if condtion is ture
            }

        }

        primes.push(n); // update prime list with the prime number

    }

    for (var index = 0; index < primes.length; index++) {
        $("#body").append(primes[index] + '<br/>');
    }

}

findPrimes(2, 150);

Upvotes: 1

Views: 59

Answers (1)

takteek
takteek

Reputation: 7110

It should be continue primes_loop instead of break primes_loop. Currently when it reaches a composite number (the first being 9 as it is incrementing by 2) it breaks out of the outer loop and stops the search entirely instead of just skipping that number.

Upvotes: 7

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