Check Prime Number In PHP

Question

My html document has the following form:

<form action="PrimeNumber.php" method="post">
Enter a number to determine if it is a prime number: <input type="text" name="numb" size="10">
<input type="submit" value="Check for Primeness">
</form>

Edit: Using a different code now but can't get it to echo a statement no matter what I do. Anyone know how I can make it echo is a prime number or is not.

<?php
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    if (isset($_POST['numb'])) {
        $num = $_POST['numb'];

        function isPrime($num) {
            if($num == 1) {
                return false;
            }

            if($num == 2) {
                return true;
            }

            if($num % 2 == 0) {
                return false;
            }

            for($i = 3; $i <= ceil(sqrt($num)); $i = $i + 2) {
                if($num % $i == 0)
                    return false;
            }
            return true;
        }
    }
}
?>

If I install the package will it still work for people viewing it who don't have the package? Thanks BTW. — user3529629, Apr 13 '14 at 18:39
I don't know what is your issue, though if you are eager to check if number is prime or not here is the algorithm written in `JavaScript` though probably you find it interesting. [Check Out](http://stackoverflow.com/questions/23045746/understanding-number-functions-in-javascript/23045785#23045785) — nanobash, Apr 13 '14 at 18:43
But even after you install the package are you sure that you will get the desired result with the above code? You need to review your code. — Vagabond, Apr 13 '14 at 18:48

score 1 · Answer 1 · answered Feb 23 '18 at 14:42

simple and easy to understand code, and working as well. do little changes according to your requirement, like assign input text value to $a variable and you good to go.

$a = 51;
for($i=2; $i < $a; $i++){
    if($a % $i == 0){
        echo "Numberis not prime.";
        break;
    }
    else{
        echo "Number is not prime.";
        break;
    }
}

score 1 · Answer 2 · answered Sep 12 '18 at 11:03

1

A simple function to check is prime number:

function is_prime($p) {
    return ($p > 1) &&  (($p%2 >= 1) && ($p%3 >= 1) && ($p%5 >= 1)) ||  in_array($p, [2,3,5]);
}

answered Sep 12 '18 at 11:03

Said Sabir

101
4

This is NOT correct at all. It returns true for 49 (7*7), 77 (7*11), 121 (11*11) and so on – GMarco24 Jun 20 '19 at 10:16

score 1 · Answer 3 · edited Jul 11 '20 at 06:52

function checkPrime($num){
      $isPrime = true;
    
    for($i = 2; $i <= sqrt($num); $i++)
    {
        if($num % $i == 0) 
        {
          $isPrime = false;
        }
    }
    if($isPrime == true)
    {
        return "$num is prime number";
    }else{
        return "$num  is not prime number";
    }
}

echo checkPrime(29);

The output is

29 is prime number

For More Details

score 0 · Answer 4 · answered Apr 13 '14 at 19:07

0

You may use the gmp package and correct your code because I got an output as 11 not being a prime number or use the following function as an alternative.

function isPrime($num) {
    if($num == 1) {
        return false;
    }

    if($num == 2) {
        return true;
    }

    if($num % 2 == 0) {
        return false;
    }

    for($i = 3; $i <= ceil(sqrt($num)); $i = $i + 2) {

        if($num % $i == 0)

            return false;
    }
    return true;
}

More information is available at the following page.

answered Apr 13 '14 at 19:07

Vagabond

877
1
10
23

I tried using that, but when I add echo statements after the return of true or false, it doesn't display anything. echo $num.'is a prime number'; – user3529629 Apr 13 '14 at 19:09
You need to use it in a if-conditional. – Vagabond Apr 13 '14 at 19:11
Could you give me a sample because nothing I'm trying is working. – user3529629 Apr 13 '14 at 20:19
For eg: `if (isPrime(11)) { echo "PRIME";} else { echo "NO";}` – Vagabond Apr 13 '14 at 20:30
if (isPrime($num) == false){ echo 'Not Prime'; } //This doesn't work? – user3529629 Apr 13 '14 at 21:57
The code does work without any problem... Check it out at this [link](http://codepad.org/GwfxeAum)... – Vagabond Apr 14 '14 at 10:09

score 0 · Answer 5 · answered Jul 28 '17 at 11:52

A simple function to help you find out if a number is a prime number

<?php 
     function fn_prime($number) {
        $i = 2; $result = TRUE;
        while($i < $number) {
            if(!($number%$i)) {
                $result = FALSE;
            }
            $i++;
        }
        return $result;
     }
?>

Check Prime Number In PHP

5 Answers5