前端学PHP之运算符，学PHP之运算符

定义

　　运算符即做运算的标识符号。PHP运算符一般分为算术运算符、赋值运算符、比较运算符、三元运算符、逻辑运算符、字符串连接运算符、错误控制运算符、递增递减运算符和数组运算符

算术运算符

+<span>(加法)
    </span><span>$x</span> + <span>$y</span>
-<span>(减法)
    </span><span>$x</span> - <span>$y</span>
*<span>(乘法)
    </span><span>$x</span> * <span>$y</span>
/<span>(除法)
    </span><span>$x</span> / <span>$y</span>
%<span>(求模)
    </span><span>$x</span> % <span>$y</span>

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赋值运算符

　　PHP的赋值运算符有两种，分别是直接赋值"="和引用赋值"&"

[1]直接赋值

　　直接赋值"="把右边表达式的值赋给左边的运算数。它将右边表达式值复制一份，交给左边运算数。换言之，首先给左边运算数申请一块内存，然后把复制的值放到这块内存中

x =<span> y
x </span>+=<span> y
x </span>-=<span> y
x </span>*=<span> y
x </span>/=<span> y
x </span>%= y

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[2]引用赋值

　　引用赋值&意味着两个变量都指向同一个数据。它将使两个变量共享一块内存，如果这个内存存储的数据变了，那么两个变量的值都会发生变化

<?<span>php 
    </span><span>$a</span> = "测试内容1"<span>;
    </span><span>$b</span> = <span>$a</span><span>;
    </span><span>$c</span> = &<span>$a</span><span>;
    </span><span>$a</span> = "测试内容2"<span>;
    </span><span>echo</span> <span>$b</span>."<br />";<span>//</span><span>测试内容1</span>
    <span>echo</span> <span>$c</span>."<br />";<span>//</span><span>测试内容2</span>
?>

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比较运算符

　　比较运算符主要用来进行比较运算

==<span>         等于 
</span>===<span>        全等
</span>!=<span>         不等
</span><><span>         不等
</span>!==<span>        不全等
</span>><span>          大于
</span><<span>          小于
</span>>=<span>         大于等于
</span><=         小于等于

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<?<span>php  
    </span><span>$a</span> = 1<span>;
    </span><span>$b</span> = "1"<span>;
    </span><span>var_dump</span>(<span>$a</span> == <span>$b</span><span>);
    </span><span>echo</span> "<br />";<span>//</span><span>bool(true)</span>
    <span>var_dump</span>(<span>$a</span> === <span>$b</span><span>);
    </span><span>echo</span> "<br />";<span>//</span><span>bool(false)</span>
    <span>var_dump</span>(<span>$a</span> != <span>$b</span><span>);
    </span><span>echo</span> "<br />";<span>//</span><span>bool(false)</span>
    <span>var_dump</span>(<span>$a</span> <> <span>$b</span><span>);
    </span><span>echo</span> "<br />";<span>//</span><span>bool(false)</span>
    <span>var_dump</span>(<span>$a</span> !== <span>$b</span><span>);
    </span><span>echo</span> "<br />";<span>//</span><span>bool(true)</span>
    <span>var_dump</span>(<span>$a</span> < <span>$b</span><span>);
    </span><span>echo</span> "<br />";<span>//</span><span>bool(false)</span>
?>

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三元运算符

　　"?:"三元运算符是一个比较运算符，对于表达式(expr1)?(expr2):(expr3),如果expr1的值为true,则此表达式的值为expr2,否则为expr3

<?<span>php 
    </span><span>$a</span> = 78;<span>//</span><span>成绩</span>
    <span>$b</span> = <span>$a</span> >=60?"及格":"不及格"<span>;
    </span><span>echo</span> <span>$b</span>;<span>//</span><span>及格</span>
?>

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逻辑运算符

　　逻辑运算符主要是进行逻辑运算

<span>and        与
or         或
xor        异或
</span>&&<span>         与
</span>||<span>         或
</span>!          非

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<?<span>php 
    </span><span>$a</span> = <span>TRUE</span>; <span>//</span><span>A同意</span>
    <span>$b</span> = <span>TRUE</span>; <span>//</span><span>B同意</span>
    <span>$c</span> = <span>FALSE</span>; <span>//</span><span>C反对</span>
    <span>$d</span> = <span>FALSE</span>; <span>//</span><span>D反对</span>
    <span>echo</span> (<span>$a</span> and <span>$b</span>);<span>//</span><span>1</span>
    <span>echo</span> "<br />"<span>;
    </span><span>echo</span> (<span>$a</span> or <span>$c</span>);<span>//</span><span>1</span>
    <span>echo</span> "<br />"<span>;
    </span><span>echo</span>(<span>$a</span> xor <span>$c</span> xor <span>$d</span>);<span>//</span><span>1</span>
    <span>echo</span> "<br />"<span>;
    </span><span>echo</span>(!<span>$c</span> ? "通过" :"不通过");<span>//</span><span>通过</span>
    <span>echo</span> "<br />"<span>;
    </span><span>echo</span>(<span>$a</span> && <span>$d</span> ? "通过":"不通过");<span>//</span><span>不通过</span>
    <span>echo</span> "<br />"<span>;
    </span><span>echo</span> (<span>$b</span> || <span>$c</span> || <span>$d</span> ? "通过":"不通过");<span>//</span><span>通过</span>
?>

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字符串运算符

　　字符串连接运算符是为了将两个字符串进行连接

[1]连接运算符(.)

<?<span>php 
    </span><span>$a</span> = 'hello'<span>;
    </span><span>$b</span> = <span>$a</span> . ' world!'<span>;
    </span><span>//</span><span>hello world!</span>
    <span>echo</span> <span>$b</span><span>;
</span>?>

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[2]连接赋值运算符(.=)

<?<span>php 
    </span><span>$x</span> = 'hello'<span>;
    </span><span>$x</span> .= ' world!'<span>;
    </span><span>//</span><span>hello world!</span>
    <span>echo</span> <span>$x</span><span>;
</span>?>

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错误控制运算符

　　PHP提供了一个错误控制运算符@,对于一些可能会有运行过程中出错的表达式，不希望出错时显示错误信息时，将@放置在一个PHP表达式之前。如果激活了track_error特性，表达式产生的任何错误信息都被存放在变量$php_errormsg中，此变量在每次出错时都会被覆盖

　　[注意]错误控制前缀@不会屏蔽解析错误的信息，不能把它放在函数或类的定义之前，也不能用于条件结构如if和foreach等

<?<span>php
</span><span>$a</span> = 1<span>;
</span><span>echo</span> @ <span>$a</span>;<span>//</span><span>1</span>
<span>$b</span><span>;
</span><span>echo</span> @ <span>$b</span>;<span>//</span><span>不报错</span>
?>

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递增/递减运算符

++<span>$x</span><span>     前递增
</span><span>$x</span>++<span>     后递增
</span>--<span>$x</span><span>     前递减
</span><span>$x</span>--     后递减

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<?<span>php
</span><span>$x</span>=10<span>; 
</span><span>echo</span> ++<span>$x</span>; <span>//</span><span> 输出 11</span>
<span>$y</span>=10<span>; 
</span><span>echo</span> <span>$y</span>++; <span>//</span><span> 输出 10</span>
<span>$z</span>=5<span>;
</span><span>echo</span> --<span>$z</span>; <span>//</span><span> 输出 4</span>
<span>$i</span>=5<span>;
</span><span>echo</span> <span>$i</span>--; <span>//</span><span> 输出 5</span>
?>

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数组运算符

　　用于比较数组

+<span>      联合
</span>==<span>     相等
</span>===<span> 　　全等
</span>!=<span>     不相等
</span><><span>     不相等
</span>!== 　　不全等

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<?<span>php
</span><span>$x</span> = <span>array</span>("a" => "red", "b" => "green"<span>); 
</span><span>$y</span> = <span>array</span>("c" => "blue", "d" => "yellow"<span>); 
</span><span>$z</span> = <span>$x</span> + <span>$y</span><span>; 
</span><span>var_dump</span>(<span>$z</span>);<span>//</span><span>array(4) { ["a"]=> string(3) "red" ["b"]=> string(5) "green" ["c"]=> string(4) "blue" ["d"]=> string(6) "yellow" } </span>
<span>echo</span> "<br>"<span>;
</span><span>var_dump</span>(<span>$x</span> == <span>$y</span>);<span>//</span><span>bool(false)</span>
<span>echo</span> "<br>"<span>;
</span><span>var_dump</span>(<span>$x</span> === <span>$y</span>);<span>//</span><span>bool(false)</span>
<span>echo</span> "<br>"<span>;
</span><span>var_dump</span>(<span>$x</span> != <span>$y</span>);<span>//</span><span>bool(true)</span>
<span>echo</span> "<br>"<span>;
</span><span>var_dump</span>(<span>$x</span> <> <span>$y</span>);<span>//</span><span>bool(true)</span>
<span>echo</span> "<br>"<span>;
</span><span>var_dump</span>(<span>$x</span> !== <span>$y</span>);<span>//</span><span>bool(true)</span>
?>

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