Data types, number types_PHP tutorial

data type, numeric type

data type

There are three data types in PHP: scalar data type, composite data type, and special data type

PHP is a weak data type language. A variable in PHP can store any type of data. The variable type is determined by the data.

Strong data type language:

The characteristic of strong data type language is that before using a variable, the variable must be declared as a variable of this type according to the type of data the variable will store.

Java example:

Define a variable to store integer data

int v1 = 100

v1 = 'one' //Report an error immediately

PHP weak data type language:

Features, variables can store any data type.

php example:

Define a variable to store integer data

$v1 = 100;

$v1 = 'one';

Scalar data type

Integer type (int, integer)

The value of the integer type is a value in the set (...-2,-1,0,1,2,3....).

The integer occupies 4 bytes (4 means not 4 bits in decimal, but 32 bits in binary)

The maximum representation range of integer type: 2147483647

Principle:

(01111111111111111111111111111111)₂=(2147483647)₁₀

Integer values ​​can also be octal or hexadecimal

Octal: starts with 0, the number cannot be greater than 7

Hexadecimal: starting with 0x, the numbers include 0 to 9, A (10), B, C, D, E, F (15)

Example:

You can use the printf() function to format the output data

Syntax:

printf('format string', data list)

Description:

The format string can contain some placeholders:

%d Decimal

%b Binary

%o Octal

%x Hexadecimal

Example 1:

Example 2:

Decimal type (float)

Numbers with decimal points are decimal types (also called precision types). PHP divides decimal types into single precision (floatsingle) and double precision (double).

float type

double type

类型	字节	最小值	最大值
Float	4	-3.402823466E 38	3.402823466E 38
Double	8	-1.7976931348623157E 308	1.7976931348623157E 308

Type

Bytes

Min. Value

Maximum value

Float

4 span>

-3.402823466E 38

3.402823466E 38

Double

8

-1.7976931348623157E 308

1.7976931348623157E 308

Integer type 4 bytes (32 binary digits) Maximum representation 2147483647

float 4 bytes (32 binary bits) 3.402823466E 38

IEEE organizational regulations (Institude Electrical Electroncity Engineer)

Constraints on floating point numbers:

0 000 0000 0 000 0000 0000 0000 0000 0000

0sign sign bit 1 bit 0 means positive number 1 means negative number

000 0000 0 The exponent index bit has 8 digits

000 0000 0000 0000 0000 0000Valid data bits Mantisa 23 bits

If the exponent bit and valid data bit are both 0, it means the data is 0, as follows:

000 0000 0 000 0000 0000 0000 0000 0000

The exponent bits are all 1, and the valid data bits are all 0, which means the data is infinite, as follows:

111 1111 1 000 0000 0000 0000 0000 0000

The exponent bits are all 1, and the valid data bits are all non-zero, which means the data is null, as follows:

111 1111 1 000 0000 0000 0000 0000 0000

The data range represented by

is determined by the exponent bit and the valid data bit.

Exponent bit:

11111110 254 We need to subtract 127 127

127th way of 2       Decimal number =>  1.7014118346046923e 38

Valid data bits:

There is a hidden 1 before the valid data bit

000 0000 0000 0000 0000 0000

1.11111111111111111111111 Decimal number =>1.99999999999 (approximately equal to 2)

The exponent bits are multiplied by the valid data bits:

1.7014118346046923e 38*2 is approximately equal to 3.402823466E 38

Example:

boolean Boolean type:

Mainly used to express the only two states of things, right, wrong, true and false

Value:

true means established

false means not true

The Boolean type value itself has no meaning and is mainly used for process control.

String

A collection of 0 or more characters

character definition method:

Method 1:

A string defined using single quotes

 

Method 2: String defined using double quotes

Method 3: Delimited string

Syntax:

$v1 = <<

Content

end of delimiter;

Example:

Note:

The start tag and end tag of the delimiter must be consistent

There can be no spaces before the closing tag

The delimiter can be understood as an html editor.

Delimiters can be divided into two categories: heredoc and nowdoc

The syntax of heredoc:

Syntax:

$v1 = <<

Content

end of delimiter;

nowdoc syntax:

Syntax:

$v1 = <<<'Delimiter starts'

Content

end of delimiter;

Example:

Note:

The use of single quotes and double quotes. Generally, if there are no variables in the string, use single quotes (the efficiency will be higher).

Composite data type

array(array)

Arrays are mainly used for storage, multiple data (variables) with certain relationships

Example:

object(object)PHP Advanced

Special data data types:

resource (resource type)

The resource type also measures a special variable. Programmers cannot perform any operations on the resource type and can only view (var_dump).

Resource types can only be created through special functions provided by PHP.

The resource type is mainly used to represent PHP’s extended resources (data outside of PHP), such as: a data connection, a result set of a data table, an external text file, etc.

null(empty)

Null is also a special variable in PHP, which means null. Generally, you can check an undefined variable, or the variable has been unset().

http://www.bkjia.com/PHPjc/1116376.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/1116376.htmlTechArticleData type, numeric data type There are three data types in PHP: scalar data type, composite data type, special data Type A weak data type language in PHP, a...