PHP - check if number is prime

Question

I\'m trying to create a function which checks whether the number is prime or not. BUT I want this function to echo to the user \'prime\' or \'NOT prime\' - and that\'s where my

Answer 1

You can print "Prime" as a return to the function to ensure nothing is printed during the function except for the condition for "NOT prime".

   class IsPrime
    {       
        function check($num)
        {
            for ($i = 2; $i < $num; $i++)
            {
                if ($num % $i == 0) 
                {
                    echo 'NOT prime';
                    break;
                }               
            }
          return "Prime";         
        }       
    }

    $x = new IsPrime();
    echo $x->check(4);

Answer 2

<?php
function primeCheck($num)
{
    if ($num == 1)
        return false;
        for ($i = 2; $i <= $num/2; $i++)
        {
            if ($num % $i == 0)
            {
                return false;
            }
        }
    return true;
}

$primeNumber = primeCheck(17);

if ($primeNumber == true)
{
    echo "Is Prime";
}
else
{
    echo "Is Not Prime";
}
?>

Answer 3

Please Check this

class IsPrime
{       
    function check($num)
    {
        for ($i = 2; $i < $num; $i++)
        {
            if ($num % $i == 0) 
            {
                return 'NOT prime';

            }

        }
        return 'Prime';           
    }       
}

$x = new IsPrime();
$result = $x->check(4);
echo $result;

Answer 4

function is_prime($number)
{
    return (bool) !preg_match('/^1?$|^(11+?)\1+$/x', str_repeat('1', $number));
}

Answer 5

You can check number is prime or not & without using loop with this function:

function is_prime($p) {

    $r1 = $p%2;
    $r2 = $p%3;
    $r3 = $p%5;

    return ($p > 1) &&  (($r1 >= 1) && ($r2 >= 1) && ($r3 >= 1)) ||  in_array($p, [2,3,5]);
}

Answer 6

As many answer pointed out, your logic code has a problem: when you get i such that num % i == 0, you print "NOT prime" and quit the loop, after that, you still print "Prime". Some guys moved echo "Prime" in if-else, it is still wrong. One way to approach, for example,

class IsPrime
{       
     function check($num)
     {
        $bCheck = True; 
        for ($i = 2; $i < $num; $i++)
        {
            if ($num % $i == 0) 
            {
                 $bCheck = False;
                 break;
            }               
        }
       if $bCheck 
          echo 'Prime';           
       else
          echo 'NOT prime'; 
     }       
  }

 $x = new IsPrime();
 $x->check(4);