Getting started with PHP - PHP syntax

1. Introduction to PHP (1) PHP: Chinese name, hypertext preprocessor, is a general open source scripting language; (2) Introduction to Dreamweaver

(3) Four delimiters

Standard style: ; Short tag style: ; By default, the short tag style is not supported. You must enable support for short tags in the PHP configuration file (php.ini) ; In the configuration file, search for "short_open_tag", change the parameter to On, and restart the Apache server; asp style: ; By default, asp style delimiters are not supported, and they must be set in the configuration file Enable support for asp tags in (php.ini); In the configuration file, search for "asp_tags", change the parameter to On, and restart the Apache server; Script style: ; PHP supports omitting the end tag. When all PHP code is after the PHP start delimiter until the end, the PHP code can be omitted; (4) PHP execution principle: The client sends a request to the server , if the request is an HTML page, the server directly sends the HTML page to the client for the browser to parse; if the request is a PHP page, the server will run the PHP page, then generate a standard HTML page, and send the generated HTML code to the client; The client parses the HTML code, but does not run the PHP code; The server does not parse the HTML, but runs the PHP code; 2. Characteristics of PHP syntax (1) The PHP statement ends with a semicolon; (2 ) PHP keywords are not case-sensitive, and variable names are case-sensitive; 3. Variables (1) Naming rules for variables: PHP must start with $, $ is not a component of the variable, it just means that the variable name of PHP will be used from now on. Begins at; In addition to $, it starts with letters and underscores, followed by letters, numbers, and underscores; (2) Assignment of variables: use "=" to assign values; (3) Destroy variables: unset($x) ; unset() destroys the variable name, and the value is destroyed by PHP's garbage collection mechanism; (4) Variable variable $a = "甄禾日道道"; $b = "a"; echo $$ b; Output: It is noon on the day of hoeing; $b saves the variable name a, so $$b is $a, and finally outputs the value of $a; (5) Constant When a value is inside the script execution cycle If a change occurs, you can declare the value as a constant using the define() keyword; Constant names cannot start with $; define("name", "Li Bai"); define("constant name", "value" , whether it is case-sensitive (true or false); ture means not case-sensitive, false means case-sensitive; By default, constant names are case-sensitive; Constants cannot be defined repeatedly, judge first when defining a constant Whether the current constant is defined or not, the defined() function determines; 4. Data type of the variable (1) Scalar type Integer type, floating point number (float and double are the same), Boolean value (TURE, FALSE), string (Single quotation marks and double quotation marks); (2) String type Single quotation mark string does not replace the variable ($name), double quotation mark string replaces the variable ($name) with the variable value; Because the single quotation mark string does not need operation, so single-quoted strings perform more efficiently; If the variable is in front or in the middle of the string, curly brackets {} are neededenclosed; The left curly brace { and $ must be next to each other, and there must be no spaces in between; The left curly brace { and $ can be interchanged; (3) conform to the type array (array), object (object); array ：$students = array('Tom', 'Jack', 'Ketty'); Index array: The subscript is based on the position of the element. The default starts from 0. You can change the starting subscript, $students[0], $ students[1]; $emp=array('name'=>'Zhang Jie', 'age'='18', 'sex'='boy'); Keyword index: Get elements by their keywords , $emp['name'], $emp['sex']; Specify array index: $index = array(1=>'a', 3=>'b', 5=>'c '); (4) Special type resource (resource): PHP's external data is called resource type; NULL (no type): no data; 5. Output statement (1) echo: can only output numbers, String; For Boolean type, TRUE can only output 1, FALSE can only output NULL; Compared with print, multiple parameters can be output at one time, and there is no return value if the output is successful; (2) var_dump(): If the variable is output , the value of the variable and the type of the variable; If the output is an array, include keys, values, and value data types; (3) print_r(): used to output an array, the output content includes the keys and values of the array, excluding Data type; (4) print: Very similar to the echo statement, only one parameter can be output at a time; Successful output will return 1, failure will return 0; 6. Comments (1) Single-line comments: // and #; (2) Multi-line comments: /* */; 7. Operators (1) Arithmetic operators: The plus sign (+) can be used to add numbers and connect strings in JavaScript; In PHP, the plus sign (+) can only do numerical operations; (2) comparison operators: === (congruent): compare values and data types; !== (not congruent): compare values and Data types are not equal; (3) Logical operators: &&, ||, !; (4) String concatenation: In PHP, the string concatenation is dot (.); Eight , Judgment statement (1) Single branch: (2) Double branch: (3) Multiple branches: (4) Multiple selection: 9. Function (1) Predefined function: PHP system function; ( 2) Custom function: Function function name (parameter) { }, call the function through the function name; (3) return: terminate the execution of the function, the function returns the corresponding data; 10. Classification of arrays (1) Classification by key : Index array and associative array; (2) Structural classification: one-dimensional array and multi-dimensional array; The above introduces the introductory learning of PHP - PHP syntax, including various aspects. I hope it will be helpful to friends who are interested in PHP tutorials.