Data type, number type _php tutorial

Data type, Number type

Data type

There are three types of data in PHP: Scalar data type, composite data type, special data type

In PHP, 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 strong data type language is characterized by the fact that a variable must be declared to be a variable of this type, based on the type of data that the variable is about to store, before it can be used.

Java Example:

Define a variable to store integer data

int v1 = 100

V1 = ' one '//Immediate error

PHP Weak data type language:

Features, variables can store arbitrary data types.

PHP Example:

Define a variable to store integer data

$v 1 = 100;

$v 1 = ' one ';

Scalar data types

integral type (int, integer)

The value of an integral type is the collection (..... -2,-1,0,1,2,3 ...) A value in the.

Integer takes up 4 bytes (4 means not 4 bits in decimal, but 32 bits in binary)

Maximum representation range for integer type: 2147483647

Principle:

(01111111111111111111111111111111) 2 = (2147483647) 10

The value of an integral type can also be octal, hexadecimal

Octal: Starting with 0, numbers cannot be greater than 7

Hex: Starting with 0x, digital contains 0 to 9, A (10), B, C, D, E, F (15)

Example:

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

Grammar:

printf (' format string ', data list)

Description

The format string can contain some placeholders:

%d decimal

%b binary

%o Octal

%x Hex

Example 1:

Example 2:

Decimal type (float)

The number with the decimal point is the decimal type (also known as the precision type), PHP for the decimal type is divided into single-precision (Float\single) and double-precision (double)

Float type

Double type

Type	Bytes	Minimum value	Maximum Value
Float	4	-3.402823466E+38	3.402823466E+38
Double	8	-1.7976931348623157E+308	1.7976931348623157E+308

Integer 4-byte (32 bits) maximum representation 2147483647

Float 4 bytes (32 x bits) 3.402823466E+38

IEEE Organizational provisions (Institude electrical electroncity Engineer)

Constraints on floating-point numbers:

0 0000 0 0000 0000 0000 0000 0000

0sign symbol bit 1 bit 0 indicates positive number 1 indicates negative number

0000 0 exponent digit 8 digits

0000 0000 0000 0000 0000 Valid Data bits Mantisa 23-bit

Both the digit and the valid data bits are 0 to represent the data 0, as follows:

0000 0 0000 0000 0000 0000 0000

The number of digits is 1, and the valid data bits are 0, which means the data is infinitely large, as follows:

111 1111 1 0000 0000 0000 0000 0000

The digits are 1, and the valid data bits are nonzero for data null, as follows:

111 1111 1 0000 0000 0000 0000 0000

Range of data represented: determined by index bit and valid data bit

Decimal point:

11111110 254 minus 127 127.

2 of 127-way decimal number = 1.7014118346046923e+38

Valid data bits:

There is a hidden 1 before the valid data bits

000 0000 0000 0000 0000 0000

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

The digits are multiplied by the valid data bits:

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

Example:

Boolean Boolean type:

It is mainly used to denote the existence of two states of things, right, wrong, true or false.

Value:

True indicates that the setting

False indicates not valid

The value of a Boolean type has no meaning in itself, and is primarily used for process control.

String

A collection of 0 or more characters

How characters are defined:

Method 1:

string defined using single quotation marks

Method 2: Use double quotation marks to define a string

Method 3: Bound string

Grammar:

$v 1 = <<<>< p=""><>

Content

End of delimiter;

Example:

Attention:

The start tag of the delimiter is identical to the closing tag

Cannot have spaces before closing tags

The delimiter can be interpreted as an HTML editor.

Delimiters can be divided into two categories: Heredoc and Nowdoc

Syntax for Heredoc:

Grammar:

$v 1 = <<<>< p=""><>

Content

End of delimiter;

Syntax for Nowdoc:

Grammar:

$v 1 = <<< ' delimiter start '

Content

End of delimiter;

Example:

Attention:

The use of single and double quotation marks, generally if the string does not have a variable using single quotation marks (high efficiency).

Composite data types

Array (arrays)

Arrays are primarily used for storage, with a number of relational data (variables)

Example:

Object (objects) PHP advanced

Special Data Data types:

Resource (Resource type)

The resource type also amounts to a special variable, the programmer cannot do anything to the resource type, only view (Var_dump),

The resource type can only be created by the special function PHP provides for us.

Resource types are primarily used to represent PHP's extended resources (data other than PHP), such as a data connection, a data table result set, an external text file, and so on.

Null (empty)

Null is also a special variable in PHP, representing NULL, generally looking at an undefined variable, or the variable being unset ().

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