Learn to have-php basic grammar-06

A string of 1 definitions

Use 0 or more characters enclosed in single or double quotation marks .

Single quotes:

there is no value for the parsed variable, capable of being escaped \ \ '

Double quotes:

the ability to parse the value of a variable can be escaped

The essence of Heredoc is to use double quotation marks to define large segments of text, but to write in another way.

The essence of Nowdoc is to use single quotation marks to define large segments of text, but to write in a different way.

A string can also be used as a series organized by multiple characters

Example:

2 string length

①,strlen

Grammar:

strlen ( variable )

Description

The number of bytes used to get a string

Support for ②, multibyte characters

The default letter holds a character in the 1 bytes occupied by any character living in .

However, for example: Kanji, a character may occupy multiple bytes, so PHP provides support for multibyte characters.

Support for multibyte characters needs to be turned on in PHP.ini .

after opening a multi-byte branch, we can use multibyte-character manipulation functions.

Mb_strlen ( variable, memory encoding )

3 string-related functions

①, Output function

Echo

Print

Print_r

Var_dump

②, finding and intercepting functions

Strstr (STR,SUBSTR)

Description

used to query substrings in the string str for the first occurrence of a substring Substr, and to intercept the last

STRRCHR (STR,SUBSTR)

Description

used to query substrings in string str for the last occurrence of a sub-string , and to intercept the last

Example:

③, find

Strpos (STR,SUBSTR)

Description

The position used to query substrings in the string str for the first occurrence of sub- str

STRrPOS (STR,SUBSTR)

Description

used to query substrings in the string str where the last occurrence of the sub- str

Example:

④, Split

Explode ( delimiter , str)

Description

Specifies the specified delimiter, splits the string str, and organizes each part into an array and returns

Example:

⑤, replace

Str_replace (Search,rep, str);

Description

in the string str , find the content represented by search and replace it with the content represented by Rep

⑥, uppercase and lowercase conversions

Strtolower ()

Strtoupper ()

Example:

⑦, removing specified characters

Trim (str", substr")

Description

used to remove substring substr on both sides of the string str .

SUBSTR can be omitted if omitted to indicate the removal of whitespace.

Example:

LTrim (str", substr");

RTrim (str", substr")

⑧,pathi NFO

Grammar:

PathInfo (Path", Option");

Description

Path is a string of file paths

The path information used to get a file ( file name, folder, file name, extension )

the option parameter is used to get the part specified in the path information

Example:

Example:

⑨,MD5 ()

Grammar:

MD5 (STR);

Description
used to encrypt the str string feed. the MD5 processing of strings of any length gets a string of length.

⑩,htmlspecialchars

Grammar:

Htmlspecialchars (str)

Description

used to convert the greater than sign less than sign in the string str to the corresponding character entity.

< < > >

Example:

Htmlspecialchars_decode (str)

Two-array preliminary 1 concept

An array is a collection of data.

arrays are primarily used to store rows with row and column characteristics ( form ) the data.

classification of 2php arrays

①, indexed arrays

The subscript of an array is an integer. Such an array is an indexed array

②, associative arrays

The subscript of an array is a string. Such an array is an associative array.

Creation of 3php arrays

①, indexed array creation

Example:

Description

the subscript of an array in PHP can be discontinuous.

Creation of ②, associative arrays

Grammar:

$arr = Array (key name = = Key value , key name = = Key value ,....);

$arr = [key name = = Key value , key name = = Key value ,....];

Description

the array elements in PHP consist of two parts, the key name (subscript ), the key value

Example:

4 Multi-dimensional arrays

a multidimensional array is supported in PHP, and if the element of an array is an array, then this is a multidimensional array.

5 array element Access

①, one-dimensional array element access

Grammar:

$ Array name [ subscript / key name ]

Example:

Access to ②, two-dimensional array elements

Grammar:

$ array name [ row subscript] [ column subscript ]

Example:

6 Length of the array

Count ()

Used to get the length of an array

Pointers to three arrays

array pointers are used to represent elements that are currently of interest.

Current ($arr) is used for the key value of the element to which the pointer is pointing

Key ($arr) is used for the name of the element that the current pointer points to

Next ($arr) moves the pointer down the array.

Prev ($arr) is used to move the pointer of an array up.

Reset ($arr); used to reset the pointer of an array ( homing , array pointers default to the first 1 elements ) .

End ($arr); used to move the pointer of an array to the last element.

Example:

Traversal of the four arrays 1for

The For loop is used to iterate through the data by using a loop control variable to simulate the subscript, only to traverse the next continuous or regular

but not The array subscript in PHP can be discontinuous and irregular, or it may be an associative array. For how associative arrays are traversed.

2foreach

①, grammar
foreach ($arr as "$key= ="$value ){

Loop Body

}

Description

$arr is the array to traverse ,$key,$value is a variable, and the variable name can be customized.

Example:

②,Foreah principle

First, the pointer to the array is reset.

reads the array element that the current pointer points to, and assigns the key name of the element to the variable $key, assigning the key value to the variable $value,

The pointer to the array is also moved down one line ( move the pointer down for the next loop ) .

foreach does not need us to control the number of loops, it automatically determines when to end the loop.

3while-each-list traversal

using the while loop, and the Each () function, thelist syntax structure is combined to iterate through the array.

①, each

Each ( array )

Description

Used to get the element key name and key value that the current pointer points to, and to represent both the index element and the relationship element, while moving the pointer down one line.

Example:

②,list

Grammar:

List ( variable ) = $arr

Description

Assigns an indexed element in an array $arr to a variable in the variable list.

Example:

③,while-each-list traversal array

③,foreach and list

Grammar:

List ( variable ) = $arr

Description

the right side of the list statement must be an array

Example:

Five array operations common functions 1 the length of the array

Count (array name)

2 getting the key names and key values for an array element

①, Array_keys ()

Get all the key names of an array element

②,array_values ()

Get all the key values of an array element

Example:

3 determine if key names and key values exist

①,array_k ey_exists (Key,arr)

used to determine if a key name exists in the array and returns true if it exists , otherwise false

②,in_array (value,arr);

used to determine if a key value exists in the array and returns true if it exists , otherwise false

Example:

4 Merging of arrays

Array_merge ( array 1, array 2...)

5 Sorting of arrays

①,sort ()

Sorting an array of key values in ascending order

②,rsort ()

descending sort of an array of key values

Example:

③,asort ();

array key values are sorted in ascending order, but the original subscript does not change

④,arsort ()

sorts the key values in descending order, but the original subscript does not change

6,extract

Used to decompress an array and convert the associated element to a variable with a key name.

Correlation algorithm of six arrays 1 sorting algorithm

①, Bubble Sort method

Principle:

②, insert Sort method

2. Search Algorithm

①, Sequential Lookup method

②, two-part search method

Premise:

Arrays must be ordered, and elements cannot be duplicated.

Learn to have-php basic grammar-06