Detailed explanation of data types of arrays in php_PHP tutorial
In php, arrays can store values of any PHP type. If no key name is specified for the given value, the current largest integer index value will be taken, and the new key name will be the value plus one, which is PHP array
has three array types:
numeric array
Array with numeric ID keys
Associative array
Each ID key in the array is associated with a value
Multidimensional array
Array containing one or more arrays
An array in PHP is actually an ordered map. A map is a type that associates values to keys. This type is optimized in many ways, so it can be treated as a real array, or list (vector), hash table (which is an implementation of map), dictionary, set, stack, queue and many more possibilities. The value of an array element can also be another array. Tree structures and multidimensional arrays are also allowed.
You can use the array() language structure to create a new array. It accepts any number of comma-separated key => value pairs.
key can be integer or string. If key is the standard representation of an integer, it is interpreted as an integer (e.g. "8" will be interpreted as 8, and "08" will be interpreted as "08"). Floating point numbers in key are rounded to integers. In PHP, indexed arrays are the same as associative arrays, they can contain both integer and string subscripts.
The value can be any PHP type.
If no key is specified for the given value, the current largest integer index value is taken, and the new key name will be that value plus one. If the specified key name already has a value, the value will be overwritten.
Using TRUE as the key name will make integer 1 the key name. Using FALSE as the key name will make integer 0 the key name. Using NULL as a key name is equivalent to using an empty string. Using an empty string as a key will create (or overwrite) a value with an empty string as the key, which is different from using empty square brackets.
Arrays and objects cannot be used as keys. Doing so will result in a warning: Illegal offset type.
Create/modify using square bracket syntax
If $arr does not exist yet, a new one will be created. This is also an alternative way to define an array. To change a value, just assign it a new value. If you want to delete a key/value pair, use unset() on it.
Note: If square brackets are given but no key name is specified, the current maximum integer index value is taken, and the new key name will be that value + 1. If there is no integer index currently, the key name will be 0. If the specified key name already has a value, the value will be overwritten.
Note that the maximum integer key name used here is not necessarily currently in the array. It just needs to have existed since the last time the array was reindexed.
Array indexes expressed as strings should always be quoted. For example, use $foo['bar'] instead of $foo[bar]. But why is $foo[bar] wrong?
The reason is that this code has an undefined constant (bar) instead of a string ('bar' - note the quotes), and PHP may define this constant later, unfortunately your code has the same name. It works because PHP automatically converts a bare string (a string without quotes and not corresponding to any known symbol) into a normal string whose value is that bare string. For example, if there is no constant defined as bar, PHP will replace it with 'bar' and use that.
Example 1
In this example, the ID key is automatically assigned:
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Example 2 In this example, we manually assigned the ID key:
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$names[0] = "Peter"; $names[1] = "Quagmire"; $names[2] = "Joe"; |
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$names[0] = "Peter"; $names[1] = "Quagmire"; $names[2] = "Joe"; |
You can use these ID keys in scripts:
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$names[0] = "Peter"; echo $names[1] . " and " . $names[2] . " are ". $names[0] . "'s neighbors";
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Example 1

PHP is a server-side scripting language used for dynamic web development and server-side applications. 1.PHP is an interpreted language that does not require compilation and is suitable for rapid development. 2. PHP code is embedded in HTML, making it easy to develop web pages. 3. PHP processes server-side logic, generates HTML output, and supports user interaction and data processing. 4. PHP can interact with the database, process form submission, and execute server-side tasks.

PHP has shaped the network over the past few decades and will continue to play an important role in web development. 1) PHP originated in 1994 and has become the first choice for developers due to its ease of use and seamless integration with MySQL. 2) Its core functions include generating dynamic content and integrating with the database, allowing the website to be updated in real time and displayed in personalized manner. 3) The wide application and ecosystem of PHP have driven its long-term impact, but it also faces version updates and security challenges. 4) Performance improvements in recent years, such as the release of PHP7, enable it to compete with modern languages. 5) In the future, PHP needs to deal with new challenges such as containerization and microservices, but its flexibility and active community make it adaptable.

The core benefits of PHP include ease of learning, strong web development support, rich libraries and frameworks, high performance and scalability, cross-platform compatibility, and cost-effectiveness. 1) Easy to learn and use, suitable for beginners; 2) Good integration with web servers and supports multiple databases; 3) Have powerful frameworks such as Laravel; 4) High performance can be achieved through optimization; 5) Support multiple operating systems; 6) Open source to reduce development costs.

PHP is not dead. 1) The PHP community actively solves performance and security issues, and PHP7.x improves performance. 2) PHP is suitable for modern web development and is widely used in large websites. 3) PHP is easy to learn and the server performs well, but the type system is not as strict as static languages. 4) PHP is still important in the fields of content management and e-commerce, and the ecosystem continues to evolve. 5) Optimize performance through OPcache and APC, and use OOP and design patterns to improve code quality.

PHP and Python have their own advantages and disadvantages, and the choice depends on the project requirements. 1) PHP is suitable for web development, easy to learn, rich community resources, but the syntax is not modern enough, and performance and security need to be paid attention to. 2) Python is suitable for data science and machine learning, with concise syntax and easy to learn, but there are bottlenecks in execution speed and memory management.

PHP is used to build dynamic websites, and its core functions include: 1. Generate dynamic content and generate web pages in real time by connecting with the database; 2. Process user interaction and form submissions, verify inputs and respond to operations; 3. Manage sessions and user authentication to provide a personalized experience; 4. Optimize performance and follow best practices to improve website efficiency and security.

PHP uses MySQLi and PDO extensions to interact in database operations and server-side logic processing, and processes server-side logic through functions such as session management. 1) Use MySQLi or PDO to connect to the database and execute SQL queries. 2) Handle HTTP requests and user status through session management and other functions. 3) Use transactions to ensure the atomicity of database operations. 4) Prevent SQL injection, use exception handling and closing connections for debugging. 5) Optimize performance through indexing and cache, write highly readable code and perform error handling.

Using preprocessing statements and PDO in PHP can effectively prevent SQL injection attacks. 1) Use PDO to connect to the database and set the error mode. 2) Create preprocessing statements through the prepare method and pass data using placeholders and execute methods. 3) Process query results and ensure the security and performance of the code.


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