模数PHP问题

I have a problem, I am trying to calculate what the lowest prime is of a number but I do not understand the result that PHP is giving me.

If I have this number

 $number = 600851475143;

Then I modulus it:

$primes = array( 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97);

    foreach($primes as $key=>$value) {    
        if($number % $value == 0 ) {echo $value; break; }
    }

Why is it that $value = 3? If $value = 3, that means that 600851475143 / 3 should be an integer, but its not. So I do not understand why that if() evaluates to true?

Using PHP 5.2.8, it fails as described in the question. It seems like the modulo operator doesn't work on big integers. You should consider using bc_mod (modulus with arbitrary precision):

<?php

$number = 600851475143;

$primes = array(2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97);

    foreach($primes as $key=>$value)
    {    
        if($number % $value == 0 ) {echo $value."<br/>"; }
        if(bcmod($number, $value) == 0) {echo "bcmod ".$value."<br/>"; }
    }

?>

The above code prints:

3

29

bcmod 71

I might be misunderstanding it, but modulo gives you the rest of a division, so e.g. 600851475143 / 3 is 200283825047 rest 2 and this is what it gives you back.

See this bug listing here

% does not not work for numbers over 2^31 (32-bit) or 2^63 (64-bit). Use BCMOD instead.