How to find prime numbers between 0 - 100?

Question

In Javascript how would i find prime numbers between 0 - 100? i have thought about it, and i am not sure how to find them. i thought about doing x % x but i found the obvious problem with that. this is what i have so far: but unfortunately it is the worst code ever.

var prime = function (){ var num; for (num = 0; num < 101; num++){     if (num % 2 === 0){         break;     }     else if (num % 3 === 0){         break;     }     else if (num % 4=== 0){         break;     }     else if (num % 5 === 0){         break;     }     else if (num % 6 === 0){         break;     }     else if (num % 7 === 0){         break;     }     else if (num % 8 === 0){         break;     }     else if (num % 9 === 0){         break;     }     else if (num % 10 === 0){         break;     }     else if (num % 11 === 0){         break;     }     else if (num % 12 === 0){         break;     }     else {         return num;     } } }; console.log(prime()); 

Answer 1

Here's an example of a sieve implementation in JavaScript:

function getPrimes(max) {     var sieve = [], i, j, primes = [];     for (i = 2; i <= max; ++i) {         if (!sieve[i]) {             // i has not been marked -- it is prime             primes.push(i);             for (j = i << 1; j <= max; j += i) {                 sieve[j] = true;             }         }     }     return primes; } 

Then getPrimes(100) will return an array of all primes between 2 and 100 (inclusive). Of course, due to memory constraints, you can't use this with large arguments.

A Java implementation would look very similar.