PHP variable types and conversions

echo &#39;<h3 id="变量类型与转换">2.变量类型与转换</h3>&#39;;
echo &#39;<hr color="green">&#39;;

//Scalar: single-valued variable, including integer, floating point, string, and Boolean.

$age = 30; //1整型 integer
$salary = 1234.56; //2.浮点 float
$name = 'peter'; //3 字符串
$isMarried = true;  //4. 布尔型,true真,false假

//Scalar output echo, print or var_dump() can view the type and value

echo $name.'的年龄是:'.$age.',工资是:'.$salary.',是否已婚:'.$isMarried;
echo &#39;<br>&#39;;
print $name; print &#39;<br>&#39;;
var_dump($name);
echo &#39;<hr color="red">&#39;;

//Composite type: multi-valued variables, including arrays and objects

$books = ['php','mysql','html','css','javascript']; //数组
$student = new stdClass(); //创建空对象$student
$student->name = '王二小';  //添加属性name
$student->course = 'php';  //添加属性course
$student->grade = 80;     //添加属性grade

//Composite variable output: print_r() or var_dump()

echo &#39;<pre class="brush:php;toolbar:false">&#39;; //格式化输出结果
print_r($books);
print_r($student);
var_dump($books);
var_dump($student);
echo &#39;<hr color="red">&#39;;

//Special Type: resource type, null

$file = fopen('demo.php','r') or die('打开失败');
echo fread($file, filesize('demo.php'));
fclose($file);

$price = null;

echo '$price is '.$price;

/**

* Variable type query, setting and detection

* 1. Type query:

* gettype($var)

* 2. Type detection:

* 2.1: is_integer(),

* 2.2: is_float(),

* 2.3: is_string(),

* 2.4: is_bool( ),

* 2.5: is_array(),

* 2.6: is_object(),

* 2.7: is_null(),

* 2.8: is_resource(),

* 2.9: is_numeric()...

* 3. Type conversion:

* 3.1: Force conversion: (int)$val,( string)$val...

* 3.2: Temporary conversion (the value conversion type remains unchanged): intval(), floatval(), strval(), val is value

* 3.3: Permanent conversion: settype($var, type identifier)

* /

$price = 186.79;
echo gettype($price);  //float/double浮点型,float和double同义
echo &#39;<hr>&#39;;
echo (int)$price;  //强制转为integer,186
echo &#39;<hr>&#39;;
echo $price;  //查看原始数据,仍是浮点型,并无变化
echo &#39;<hr>&#39;;
echo gettype($price);  //原始类型仍为double,并未发生变化
echo &#39;<hr>&#39;;
echo intval($price);  //临时将值转为整型,输出:186
echo &#39;<hr>&#39;;
echo $price; //输出原值,仍为186.79,原值并未发生变化
echo &#39;<hr>&#39;;
settype($price,&#39;integer&#39;);  //永久转为integer,返回布尔值
echo $price;  //查看值:186
echo &#39;<hr>&#39;;
echo gettype($price);  //类型为integer
echo &#39;<hr>&#39;;
echo is_integer($price)? &#39;Integer&#39; : &#39;Double&#39;; //Integer整型
echo &#39;<hr>&#39;;
//is_numeric():判断是否是数字或数字型字符串
var_dump(is_numeric(100));
var_dump(is_numeric(&#39;200&#39;));
var_dump(is_numeric(&#39;200php&#39;));