What do php data types mean?

In PHP, a data type uses a set of attributes to describe its defined data unit. The data type of PHP is determined by the context of the program, that is, the specific type is determined by the stored data. It is mainly divided into Scalar data types, composite data types, and special data types.

The operating environment of this tutorial: windows10 system, PHP7.1 version, DELL G3 computer

What does php data type mean

1. Introduction to data types

1. PHP is a weak type checking language. The data type is determined by the context of the program, that is, the specific type is determined by the stored data

2. Three types of data types: scalar data type, composite data type and special data type

3. Scalar data type

boolean Boolean

integer integer

float/double floating point type

string string

4, composite data type

array array

object object

5 , Special data type

resource resource

NULL empty

2. Scalar data type

Boolean

1. Save a logical true or false

2. The following situations can also be regarded as false:

  Boolean value false, integer value 0, floating point value 0.0, empty string and string "0",

Array without member variables, object without unit, NULL

<?php 
//布尔型数据
$a = true;
$b = false;
//var_dump()函数可以返回表达式的类型和值
var_dump($a);//结果为  bool(true)
echo "<br>";
var_dump($b);//结果为  bool(false)
 ?>

Integer type (integer)

1. It can only contain integers, and symbols can be used Represents positive and negative numbers

2. Unsigned integers are not supported in PHP

//整型数据
$a = +3;
$b = -5;
var_dump($a); //结果为  int(3) 
echo "<br>";
var_dump($b);//结果为  int(-5)
echo "<br>";
echo $a+$b;//结果为  -2
echo "<br>";

Floating point type (float/double)

1. Floating point type is used to store decimals The number is an approximate numerical value

2. Scientific notation: 10.1e10

//浮点型数据
$a = 1.56;
$b = 1.5e3;
var_dump($a); //结果为  float(1.56) 
echo "<br>";
var_dump($b);//结果为  float(1500)

String type (string)

1. Single quotation marks

  Variables appearing in single quotes will be output as they are, and the PHP engine will not parse them, so single quotes are the most efficient in defining strings

2, Double quotes

  Contained in double quotes The variable will be automatically replaced with the variable value

3. The delimiter is

. The delimiter is followed by specifying an identifier to indicate the beginning, and finally the same identifier to end. The string

 The end identifier must start from the first column of the line, and it cannot contain any other characters except a semicolon

//字符串型
$str = '字符串型';
echo &#39;str是$str <br>&#39;;
//结果为 str是$str     单引号变量保持原样输出
echo "str是$str <br>";
//结果为 str是字符串型  双引号会解析其中的变量
$str2 = <<<str2
这是定界符中的文字
str2;
echo $str2;
//结果为  这是定界符中的文字

3. Composite data type

Array (Array)

1. An array is a collection of related data, arranged in a specific way to form a whole

2. It can be the same data type, or it can be Different data types

3. In PHP, the index of an array can be a number or a string

//相同类型元素
$array1 = array(1,3,5,7,9);
//不同类型元素
$array2 = array(1,'hello',true,3.14);
//索引是数字
$array3 = array(1=>'a',2=>'b',3=>'c');
//索引是字符串
$array4 = array('a'='苹果','b'=>'香蕉','c'=>'桔子');

4. Special data types

Resource(Resource)

## 1. Resource is a special variable type, which holds references to external data sources, such as files, database connections, etc., until the communication ends

2. Database persistent connection is a It is a special resource that will not be released by the garbage collection system and needs to be released manually. Assignment

3. After assigning a value to a variable, use the unset() function to clear it

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