PHP number_format displaying incorrectly

New to programming and taking a PHP course. I wrote a very small program to test out the number_format function. Here is my code:

$num = 9876543210123456789; 
$result = number_format($num);
echo = $result;

The output is: 9,876,543,210,123,456,512

I'm sure it has something to do with the length of $num. But haven't been able to find the exact explanation/reason why this happens.

Solution

You're seeig a different number because the number you have provided is large enough to cause an overflow on your system. Try with a smaller number

<?php
$num = 9876543210123; 
$result = number_format($num);
echo  $result;                    // will show as expected, with formatting

Even if you don't use number_format on that number, your number will still cause overflow. Try this

$num = 9876543210123456789; 
echo  $num;   // not what you see above

Also see:

What's the maximum size for an int in PHP?