有个不太明白的地方

第一句你用三个等号试一试？

@qiayue 我知道如果===就是false，但是不太明白两个怎么可能又==又!==

所以!==是not ===的意思？

@kennedy32 是的，!=才是not ==的意思。

@kennedy32 ！先！再==，所以就是！（==），表示a和b不相等

RTFM ...

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If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically. These rules also apply to the switch statement. The type conversion does not take place when the comparison is === or !== as this involves comparing the type as well as the value.

<?php
var_dump(0 == "a"); // 0 == 0 -> true
var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true
var_dump(100 == "1e2"); // 100 == 100 -> true

switch ("a") {
case 0:
echo "0";
break;
case "a": // never reached because "a" is already matched with 0
echo "a";
break;
}

var_dump("1" == "01"); // 1 == 1 -> true
var_dump("10" == "1e1"); // 10 == 10 -> true

对这两句话感到绝望了……

@gDD 感谢3楼，正解。

其他楼的人要么把问题简单化，要么把问题复杂化

==是等于 !=是不等于
===是类型和数值都相等，曰恒等
!==是类型或数值不相等

1、==或者!=，手册：如果比较一个整数和字符串，则字符串会被转换为整数。
2、!==是===的相反，会同时比较值和类型的。