PHP gives incorrect results when formatting long numbers

Question

I am working with huge numbers for website purposes and I need long calculation. When I echo a long number I don't get the correct output.

Example

// A random number
$x = 100000000000000000000000000;

$x = number_format($x);
echo "The number is: $x <br>";
// Result: 100,000,000,000,000,004,764,729,344 
// I'm not getting the value assigned to $x

Answer 1

Your number is actually too big for php standard integers. php uses 64 bit integers which can hold values within range -9223372036854775808 (PHP_INT_MIN) to +9223372036854775807 (PHP_INT_MAX).

Your number is about 87 bits long which simply is too much.

If you really need such big numbers you should use the php BC math types, explained in the manual: http://php.net/manual/en/ref.bc.php

If you just want to format a string formed like a huge number then use something like this:

function number_format_string($number) {
    return strrev(implode(',', str_split(strrev($number), 3)));
}

$x = '100000000000000000000000000';

$x = number_format_string($x);
echo "The number is: $x\n";

// Output: The number is: 100,000,000,000,000,000,000,000,000

Edit: Added strrev() to function because the string needs to be reversed before splitting it up (thanks to @ceeee for the hint). This ensures that the delimiter is placed at right position when length of input is not divisible by 3. Generated string needs to be reversed afterwards again.

Working example can be found at http://sandbox.onlinephpfunctions.com/code/c10fc9b9e2c65a27710fb6be3a0202ad492e3e9a