Random number that is 15 characters long and positive

Question

I am trying to make random numbers that are exactly 15 characters long and positive using php. I tried rand(100000000000000, 900000000000000) but it still generates negatives and numbers less than 15. Is there another function I am missing that can do this, or should I just use rand(0, 9) 15 times and concatenate the results?

For what it's worth, `rand` isn't broken, it's just that the numbers you are using are larger then the size of an `int` on your machine which is why you're seeing odd results. — Mike Park, Jan 02 '13 at 23:55
possible duplicate of [Using long int in PHP](http://stackoverflow.com/questions/8647125/using-long-int-in-php) — Peter O., Jan 03 '13 at 01:32

score 9 · Accepted Answer · answered Jan 02 '13 at 23:49

9

$i = 0;
$tmp = mt_rand(1,9);
do {
    $tmp .= mt_rand(0, 9);
} while(++$i < 14);
echo $tmp;

answered Jan 02 '13 at 23:49

Tigger

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int mt_rand ( int $min , int $max ) is the way to go. I would use this answer. +1 – ROY Finley Jan 02 '13 at 23:52
@ROYFinley what is special about `mt_rand()` ? – Eboubaker Jun 08 '20 at 19:49
1

@ZOLDIK : Before [PHP 7.1 there were issues](https://stackoverflow.com/a/28760905/1291879). These have now been resolved with `rand()` becoming an alias for `mt_rand()`. – Tigger Jun 08 '20 at 23:41

score 3 · Answer 2 · answered Jan 02 '13 at 23:50

3

You are using a 32 bit platform. To handle these integers, you need a 64bits platform.

You can do the rand two times and save it as a string, like this:

$num1 = rand(100000,999999);
$num2 = rand(100000,999999);
$num3 = rand(100,999);
$endString = $num1.$num2.$num3;

PS. I like tiggers solution better than mine.

answered Jan 02 '13 at 23:50

Green Black

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safe to go till 2bil (10chr) so a mt_rand for 7 digits and another one for 8 digits will do it, also 99999999 instead of 9000000 – CSᵠ Jan 02 '13 at 23:54
You are right. I wasn't sure about the number, so I played it safe. – Green Black Jan 02 '13 at 23:56
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max=2,147,483,647 so 9 effective digits – CSᵠ Jan 02 '13 at 23:57

Josh Brody · Answer 3 · 2013-01-03T00:01:52.850

1

Here you go.

function moreRand($len) { 
    $str = mt_rand(1,9);
    for($i=0;$i<$len-1;$i++) { 
        $str .= mt_rand(0, 9);
    }
    return $str;
}
echo moreRand(15);

Edit: If you want to shave .00045s off your execution time,

 function randNum() { return abs(rand(100000000000000, 900000000000000)); }

edited Jan 03 '13 at 00:01

answered Jan 02 '13 at 23:49

Josh Brody

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Keep in mind this could return 0 as the first 'digit', which technically would be a 14 digit number. – Supericy Jan 02 '13 at 23:59
Whoops. Attention deficit. Fixed. – Josh Brody Jan 03 '13 at 00:03

Supericy · Answer 4 · 2013-01-02T23:55:19.343

1

Keep in mind that this will return a string, not an actual integer value.

function randNum($length)
{
    $str = mt_rand(1, 9); // first number (0 not allowed)
    for ($i = 1; $i < $length; $i++)
        $str .= mt_rand(0, 9);

    return $str;
}

echo randNum(15);

edited Jan 02 '13 at 23:55

answered Jan 02 '13 at 23:50

Supericy

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Random number that is 15 characters long and positive

4 Answers4