PHP operation method

Question

<?php

$x = 5;

$y = 6

$water = $y-- $x--;

echo $water;

The result is 13 Not sure? Find the algorithm for operation = 13

##$paper = $x $x ;

$water = $y-- $x--;

##echo $water $paper;

?>

Answer 1

I said I had a similar question before, but the idea is actually the same. I hope it will be helpful to you
https://www.php.cn/blog/detail/13861.html