The change in string to int comparison mentioned above (e.g. '' == 0 now equates to false) has some other nasty consequences:
$a = '';
// php 8
if ( $a < 0 ) echo 'true'; // echos true
if ( $a < -1) echo 'true'; // echos true
if ( $a < -100 ) echo 'true'; // echos true
// php 7
if ( $a < 0 ) echo 'true'; // no output
if ( $a < -1) echo 'true'; // no output
if ( $a < -100 ) echo 'true'; // no output
So in a situation where you may have a web form input and expected an empty value to equate to 0, watch out not only for == 0, != 0, and <= 0 comparisons, but ALL < or <= comparisons to negative integers.
