PHP basic grammar rules sorting out

Basic PHP syntax:

1. PHP variables

php variables must start with "$", for example: $name, $age

cannot start with numbers, and finally follow the camel case naming method

Variables written in "" quotation marks are best enclosed in { } to avoid characters at the end that are not parsed.

2. PHP data type

Scalar data type: string, integer, floating point, Boolean

Composite data type: array , Object

Special data type: resource, NULL

1, Integer type

Value range: -2.1 billion~2.1 billion

2. Floating point type

##Value range: -1.7E-308~1.7E 308

Since floating point numbers cannot be converted into exact binary, sometimes errors will occur during transportation, for example: (0.7 0.1) *10==8 The result is false

3. String type

3-1. Double quotes

Double quote parsing variables The value of
3-2, single quote

The name of the single quote parsed variable

3-3, long string

$Str = ...... Fill in the string content

heredoc ; The ending "heredoc" must start on a new line and end with a semicolon

3-4, resource type

Operations for third-party plug-ins, such as calling mysql database, etc. , third-party content is called resources

3-5, Boolean type

There are only two types of values, true or false

3-6. NULL type

If the variable does not exist, NULL is returned. The null type has only one value, which is NULL

3-7. Array

a. Classification of arrays

1. Index array

The subscript of the array is a positive integer starting from 0, so The array is called the "index array"

$arr=array(10,20,30,40);

$arr[0]=10;

2. Associative array

The subscript of the array is a string. Such an array is called an "associative array"

$arr=array("name"=>"Tabb ","sex"=>"gender","age"=>"22");

Since the associative array does not have an integer subscript, it is not suitable to use a for loop to traverse

3. Mixed array

Array subscripts include both integers and strings. Such an array is called a "mixed array"

$arr = array("name" => "tabb", "age" => "20", "tom", 20);

echo $arr[0] The output result is "tom"; Description The integer subscript is calculated starting from "tom"

b. Array Creation

1. Use the array() function to create an array

Use the "=>" overload symbol to specify a subscript for the array element

If the array element does not specify a subscript, its subscript is, the current maximum index is 1, example:

$arr=array(20=>"tabb",2=>"28",20,"tom") The index of "20" is 21. If they are all character subscripts, then For elements without a specified subscript, the index starts from 0

Use array to create an array:

$arr ​​= array([$key=>]$value,[$key=>]$ value,...);

2. Use [] to create an array

$arr["key"]=$value

No Like js, you don't need to declare an empty array first. If the specified array does not exist, the array will be automatically created

[ ] When the content of the square brackets is empty, the array will be created

$arr[ ]= 30;

If the array does not exist, an array will be created and the first element will be added.

If the array exists, the subscript of the element added to the array will be the largest integer subscript in the array. Standard 1

c, multi-dimensional array

array(array(1,2,3,4),1,2,3,array(1, 2,3,4))

Use [ ] brackets to quickly create a multi-dimensional array:

$arr[ ][ ][ ][ ]=10; Quickly create a 4-dimensional array

d, array related functions

1, print_r()

Print easy-to-understand information about variables

If the array or object is given, display the keys and elements according to a certain format

2. unset()

Delete the array elements, delete the It is the value of the array element, and the subscript still exists. Unlike js, the length remains unchanged. After the element is deleted here, the array length changes.

Delete the variable

3, count( )

Calculate the number of cells in the array or the number of attributes in the object

4. foreach() can only traverse the array

foreach( $arr as [$key=>]$value ){ } If it is an index array, [$key=>] does not need to be included

3. PHP data type judgment

1. var_dump()

Print variables For related information, multiple variables can be printed, separated by "," commas

2. is_*() A set of methods to determine variable types, returning a Boolean value

is_bool(): Determine whether the variable is a Boolean type

is_int(): Determine whether the variable is an integer type

is_float (): Determine whether the variable is a floating point type

is_numeric(): Determine whether the variable is of numeric type

s_string(): Determine whether the variable is of string type

is_array(): Determine whether the variable is of array type

is_object(): Determine whether the variable is of object type

is_null(): Determine whether the variable is of empty type

is_resource(): Determine whether the variable is of resource type

3. isset()

Check whether the variable is set

Return value: If the variable exists and is not equal to NULL, return true, otherwise, return false

4. empty()

Detect whether a variable is empty, such as "", 0, "0", null, array(), var $var and Objects without any attributes will be considered empty. If it is empty, the return value is TRUE

4. Data type conversion

(1) Conversion For bool value (bool)

$a = "0";

$result = (bool)$a;

var_dump($result) The result is : bool(false)

These data are false when converted to bool values: 0, 0.0, "", "0", array(), null

The resource type is always converted to bool. true

(2) Convert to integer value (int) (int)$name

1. If the string starts with a value, convert the integer part For integer values, remove the following characters

2. If it is not a string starting with a value, convert it to 0

3. The bool value true is converted to 1, false is converted to 0, and null is converted For 0

(3) Convert to floating point value (float) (float)$name

1. If the string starts with a numerical value, convert the numerical part For a numerical value (including the floating point part), remove the following characters

2. If it is not a string starting with a numerical value, convert it to 0

3. The bool value true is converted to 1, and false is converted to 0, null is converted to 0

(4) converted to string (string) (string)$name

1.null, false is converted to "", empty String

2.true is converted into the string "1"

5. Operator priority

(1) Numeric operators ( , -, / ,*,%, ,--)

The usage method is basically the same as that in js

(2)String operator

"."dot operator Indicates the string link character, which is similar to using " " to splice strings in js

$a="abc";

$b=$a.100 Or use ".=" to express Link strings with yourself: $a.=100

(3) Assignment operators (=, =, -=, *=, /=, %=) are basically the same as js

(4) Comparison operators (>, =,

Example: 10= = "10px" The result is: true; in operations involving numbers, "10px" will be converted to a numerical value first

Example: 10===="10px" The result is: false; Congruent comparison, including data types

(5) Logical operators (&&, ||, !) are basically the same as js

(6) Ternary operator (expression? Result 1: Result 2) Basically the same as js

(7) Operator priority

Recommended video tutorial: PHP video tutorial

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