get prime numbers and print

[sasori]

hi , how to get the prime numbers of the positive integer input and print them?

 

here's what i have at the moment

function getPrime($num){
  if((int)$num == $num && (int)$num > 0){
    for($i = 2; $i < $num; $i++){
      for($j = 2; $j < $i; $j++){
        if($i % 2 == 1){
          echo $i.'<br />';
        }
      }
    }
  }
}

displayPrime(10);

 

the ouput should be

 

2,3,5,7

but the output apparently, is

 

3
5
5
5
7
7
7
7
7
9
9
9
9
9
9
9

 

how to solve this?

[dragon_sa]

hers a function that will work

 

<?php
function get_primes($number) {
    $primes = array(2);
    $x = 3;
    while($x < $number) {
        $isprime = true;
        foreach($primes as $val) {
            if($x % $val == 0) {
                $isprime = false;
            break;
            }
        }
        if($isprime) {
            $primes[] = $x;
        }
        $x+=2;
    }
    foreach($primes as $val) {
		echo $val."<br>";
    }
     
}
get_primes(20);
?>

[Psycho]

Yeah, that's not going to work. The only way I think would work would be to start at 2 and work your way up. Then for each number you need to test if it is divisible by any of the previous prime numbers. If not, then that number is prime and add it to your result. Then move to the next number up.

[Psycho]

Not sure about dragon_sa's solution, but I decided to give it a whack and came up with the following. I've tested it and confirmed it works. It returns an array of all the prime numbers up to and including the target number

function displayPrime($target)
{
    if((int)$target != $target || (int)$target < 2) { return false; }
    $primes = array(2);
    for($num = 3; $num <= $target; $num+=2)
    {
        $isprime = true;
        foreach($primes as $prime)
        {
            if($num % $prime == 0) { $isprime = false; break; }
        }
        if($isprime) { $primes[] = $num; }
    }
    return $primes;
}

$result = displayPrime(55);