Scalar data type: It is the most basic unit in the data structure and can only store one data
Boolean type: boolean String type: string Floating point type: float Integer type: integer
Two composite types:
array() Array
object Object
Two special types
resource Resource type
null Empty
The function to determine the type gettype();
##Integer type: Integer is A number without decimals,
1. The integer must have at least one digit (0-9)
2. The integer cannot contain commas or spaces
3. The integer is not The decimal point
4. The integer can be a positive or negative number
5. The integer type can be specified in three formats: decimal, hexadecimal (prefixed by 0x) or octal (prefixed by 0x is 0)
<?php
$x = 5985;
var_dump($x);
echo "<br>";
$x = -345; // 负数
var_dump($x);
echo "<br>";
$x = 0x8C; // 十六进制数
var_dump($x);
echo "<br>";
$x = 047; // 八进制数
var_dump($x);
?>
Note: In the above code, we test different numbers. The PHP var_dump() function returns the data type and value of the variable
String type:
A string is a sequence of characters, like "Hello world!"
<?php
$x = "Hello world!";
echo $x;
echo "<br>";
$x = 'Hello world!';
//echo $x;
var_dump($x);
?>
Note: Using var_dump() output, we have been told that 'hello wordl!'
Yes A string type with a length of 12
Floating point type
A floating point number is a number with a decimal part, or in exponential form
<?php
$x = 10.365;
var_dump($x);
echo "<br>";
$x = 2.4e3;
var_dump($x);
echo "<br>";
$x = 8E-5;
var_dump($x);
?>
Note: 2.4e3 This kind of thing is written in scientific notation
2.4e5 = 2.4*10^5 That is equal to 2.4 times 10 raised to the fifth power
Boolean type ：
The values of Boolean type are only true and false
<?php
$x = true;
$y = false;
var_dump($x);
echo "</br>";
var_dump($y);
?>
Note: Boolean type is generally used for conditional judgment
Array type array
Arrays can store multiple values in one variable
<pre>
<?php
$cars=array("Volvo","BMW","Toyota");
var_dump($cars);
?>
</pre>Note: This is just a simple array, we will talk about array traversal later
Object: object
1. The object data type can also be used to store data
2. In PHP, the object must be declared
<?php
class Car{
var $color;
function Car($color="green") {
$this->color = $color;
}
function what_color() {
return $this->color;
}
}
?>Note: First, you must use class Keyword declares a class object. Classes are structures that can contain properties and methods.
Then we define the data type in the class, and then use the data type in the instantiated class:
In the above example, the PHP keyword this is a pointer to the current object instance, not to any Other objects or classes
NULL:
1. The special NULL value indicates that a variable has no value. The only possible value of the NULL type is NULL
2. A variable is considered NULL
in the following situations
(1). Assigned to NULL
(2). Not yet assigned
(3). Unset()
3.NULL cannot be written to null
is_null
is_null() function detects whether the variable is NULL. If the variable is NULL, it returns TRUE, otherwise it returns FALSE
<?php
header("Content-type: text/html; charset=utf-8");//设置编码
$var = NULL;
if(is_null($var)){
echo '$var 为 NULL';
} else {
echo '$var 变量非 NULL';
}
?> Resource: resource
Resource is a special variable type that saves a reference to an external resource: such as an open file, database connection, graphics canvas area, etc. Resources are created and used through specialized functions
<?php
if(!file_exists("test.txt")){
$fh = fopen("test.txt","w"); //打开文件
echo get_resource_type($fh); // 输出：stream
fclose($fh); //关闭文件
}
?>Because resource type variables save special handles for opening files, database connections, graphics canvas areas, etc., other types of values cannot be converted into resources
Next Section