PHP type conversion php7 PHP environment construction PHP from entry to proficiency

php is a weakly typed language. During the operation, the data will be converted into data that can be processed by the operator according to the operator.

1. Automatic conversion

1. if($a | number) { . . . } //The variables or numbers in the if will be automatically converted to Boolean
2. Arithmetic operators will turn the data into numerical processing

<code><span>$a</span> = <span>"3"</span>;
<span>$b</span> = <span>"5"</span>;
<span>$c</span> = <span>$a</span> + <span>$b</span> ;
var_dump(<span>$c</span>);<span>//</span><span>8</span>  integer
</code>

<code>3.  连接运算符. 转成字符串类型
</code>

<code><span>$str</span> = <span>'123'</span>.<span>true</span>.<span>'abc'</span>;<span>//</span><span>1231</span>abc string </code>

<code>4. 比较运算符，分几种情况
</code>

①Comparison of two numbers – normal situation
②If one of the data is of Boolean type, convert them all to Boolean type for comparison true>false
③If there is no Boolean type in the data, but one of the data is a number, convert it to a number and compare
④ Both sides are numeric strings, convert them into numbers for comparison
⑤Both sides of the comparison operator are string types. ASCII values ​​are compared sequentially starting from the first character. The subsequent comparison stops if the value is larger.

Some conversion rules:
“12” –> 12
“1.2” –> 1.2
"1.2a" - –> 1.2
"a1.2" —> 0
"1.1a1" —> 1.1
"0" —> false
"1" —> true
0 —> false
"0.0" —> true
"abc" —> 0
"" —> 0
"" - >false

<code><span><span><?php </span>header(<span>"content-type:text/html;charset=utf-8"</span>);
<span>$name</span> = <span>"tom"</span>;
<span>if</span>(<span>$name</span>)
{
    <span>echo</span><span>'$name为真'</span>.<span>'<hr>'</span>;
}<span>else</span>
{
    <span>echo</span><span>'$name为假'</span>.<span>'<hr>'</span>;
}



<span>//1.在算数运算符中的类型转换 :会转换成数字进行计算</span><span>$a</span>  = <span>"1.1"</span>;<span>//"1.1a" 会转换成1.1 , "a1.1"会转换成0</span><span>$b</span>  = <span>"7"</span>;

<span>$c</span> = <span>$a</span> + <span>$b</span> ;
<span>echo</span><span>$c</span>,<span>" "</span>,getType(<span>$c</span>),<span>'<hr>'</span>;<span>//12 double</span><span>//连接运算符.其结果是字符串类型</span><span>$a</span> = <span>5</span>;
<span>$b</span> = <span>true</span>;<span>// true 转换为 1 ,  false 转换成 0</span><span>$c</span> = <span>$a</span>.<span>$b</span> ;
<span>echo</span><span>$c</span>,<span>" "</span>,getType(<span>$c</span>),<span>'<hr>'</span>;<span>//51 string</span><span>//比较运算符,其结果一定是true或false</span><span>$a</span> = <span>false</span> ;

<span>$b</span> = <span>5</span>;

<span>//如果两边至少一个布尔值，则把非布尔值数据转为布尔值比较，其结果类型也是布尔</span><span>$c</span> = (<span>$a</span> $b</span>);<span>//这里$b转为true , $c = false <span>echo</span><span>$c</span>,<span>" "</span>,getType(<span>$c</span>),<span>'<hr>'</span>;<span>//1 boolean</span><span>//比较运算符中,两边不存在布尔类型但存在数字，则都转为数字类型比较</span><span>$a</span> = <span>5</span> ;
<span>$b</span> = <span>"abc"</span>;<span>//$b 要转为数字比较，这里为0 </span><span>$c</span> = (<span>$a</span> > <span>$b</span>);
<span>echo</span><span>$c</span>,<span>" "</span>,getType(<span>$c</span>),<span>'<hr>'</span>;<span>//1 boolean</span><span>//比较运算符中两边都是字符串类型</span><span>$a</span> = <span>"abc"</span> ;
<span>$b</span> = <span>"abd"</span>;
<span>$c</span> = (<span>$a</span> $b</span>);<span>//从首个字符开始依次比较ASCII值，哪个大就停止后续比较</span><span>echo</span><span>$c</span>,<span>" "</span>,getType(<span>$c</span>),<span>'<hr>'</span>;<span>//1 boolean</span></span></code>

2. Force conversion

<code><span>$a</span> = <span>11.5</span>;
<span>$b</span> = (int)<span>$a</span>;<span>//强制转换成int赋值给$b</span><span>echo</span><span>$a</span>.<span>" 类型："</span>.getType(<span>$a</span>).<span>'<hr>'</span>;<span>//11.5 类型：double</span><span>echo</span><span>$b</span>.<span>" 类型："</span>.getType(<span>$b</span>).<span>'<hr>'</span>;<span>//11.5 类型：double</span><span>$c</span> = (string)<span>$a</span>;
<span>echo</span><span>$c</span>.<span>" 类型："</span>.getType(<span>$c</span>).<span>'<hr>'</span>;<span>//11.5 类型：11.5 类型：string</span><span>$d</span> = (boolean)<span>$a</span>;
<span>echo</span><span>$d</span>.<span>" 类型："</span>.getType(<span>$d</span>).<span>'<hr>'</span>;<span>//1 类型：boolean</span><span>$e</span> = (float)<span>$b</span>;<span>//强制转换成浮点数</span><span>echo</span><span>$e</span>.<span>" 类型："</span>.getType(<span>$e</span>).<span>'<hr>'</span>;<span>//11 类型：double</span>setType(<span>$c</span>,<span>"float"</span>);
<span>echo</span><span>$c</span>.<span>" 类型："</span>.getType(<span>$c</span>).<span>'<hr>'</span>;<span>//11.5 类型：double</span></code>

3. Type-related functions

1. var_dump(): Output the complete information of a variable
2. getType(): Get the type name of a variable, The return is a type name string
3. setType(variable, "target class type"); Set the type of a variable
4. isset() Returns TRUE if the variable exists and the value is not NULL, otherwise returns FALSE.
5. empty Determine whether a variable data is empty
6. unset() Destroy a variable
7. is_int()
8. is_numeric() —1, 1.2, "1.2", "12" are all true
9. is_array() is_scalar— Basic data type: string float int boolean
10. is_null — Check whether the variable is NULL

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The above introduces the type conversion of PHP, including PHP content. I hope it will be helpful to friends who are interested in PHP tutorials.