How do you calculate $cup to be equal to 13 by computer calculation?

Question

$cup Computer calculation is equal to 13. How to calculate it?

Answer 1

<?php

$x = 5;

$y = ++$x;

$z = $x + $y;

echo "{$z} </ br>";

echo "{$x} </br>";

echo $y;

?>

//You will get a plus sign for $y = ++$x; this code Change to the front and change to the back. Watch for changes. You will understand after thinking about it a few times

Answer 2

<?php
$x = 5;
$y = 6;
$foo = $x++ + $x--; //$x和$y不变
$bar = ++$y + ++$x; //$x=6 $y=7
$cup = $x-- + $y--; //$x和$y不变   6+7=13