2018-05-23-不使用临时变量，交换两个变量的值

<?php

$a = "a";

$b = "b";

// 拼接
$a .= $b;

// 截取
$b = substr($a, 0, (strlen($a) - strlen($b)));

$a = substr($a, strlen($b));


echo "<hr/>";

// str_replace

// str_replace($search, $replace, $subject)
$b = str_replace($b, "", $a);
$a = str_replace($b, "", $a);


echo "<hr/>";

// list & array

list($b, $a) = array($a, $b);

echo "<hr/>"

// 异或运算-字符串数字合适使用

$a = $a ^ $b;

$b = $b ^ $a;

$a = $a ^ $b;


// 数字

$a = 3;
$b = 5;

$a = $a + $b;
$b = $a - $b;
$a = $a - $b;