


Intimate contact with PHP - PHP syntax study notes 1_PHP tutorial
1. PHP script code tags
PHP script is the content included in a pair of special tags in the file. For example, ASP is "", PHP can be regarded as "< ;?...?>".
However, in order to adapt to the XML standard to embed PHP into XML or XHTML, PHP does not recommend using the short form "...?>" and recommends using the long form tag " php...?>”
In addition, the PHP code block also supports the tag form of .
2. PHP command delimiter
Each statement in PHP needs to be separated by a semicolon ";", but for the PHP end mark "?>", because It automatically implies a semicolon, so there is no need to append it.
So, the format of a PHP script can be as follows:
/*
…………;
…………;
…………;
………
*/
//Note that the last line can have no semicolon
?>
3. PHP comments
PHP multi-line comments Use "/* ......... */"
Use "#" or "//" for single-line comments
Four, PHP output
Use "" in ASP to quickly output a single line, or use ""
In PHP Use "echo()" or "print()" directly, such as:
echo "a";
echo (b);
echo ("c");
echo d;
?>
will be output as "abcd", and all the above four types can be output normally.
But this is impossible in ASP, especially when echo "a"; and echo d; are both output as strings themselves. This requires understanding PHP variable definitions.
5. PHP variables
Like ASP, PHP variables can be used directly without defining them first. The type of the variable is automatically generated when assigning a value.
Various variables in PHP are distinguished by adding "$" before the variable name.
$a="123";
echo a;
echo $a;
?>
The input is "a123"
6. The difference between single quotes and double quotes in PHP
$a="123";
echo "$a";
echo '$a';
?>
The output is "123$a", where echo "$a" The value of variable a is output, and echo '$a' outputs the string itself in single quotes.
$a="123";
echo "$a'$a'";
?>
The output is "123'123'" not "123$a". Although it is '$a', the variable placed under double quotes is still replaced.
So, it can be concluded that as long as the variables are in double quotes, they will be replaced; while those in single quotes will not be replaced.
If the content in double quotes needs to be escaped, use the "" prefix, such as "\", "$", """. So to enter "123$a", it is
$a="123";
echo "$a$a";
?>
Another example:
$a="123";
echo "$a$a"\";
?>
The output is "123$a"".
What you need to pay attention to when transferring from ASP to PHP:
1. It is easy to forget to write the separator comma ";".
2 , Definition and use of variables
3, Usage of single quotes and double quotes.

What’s still popular is the ease of use, flexibility and a strong ecosystem. 1) Ease of use and simple syntax make it the first choice for beginners. 2) Closely integrated with web development, excellent interaction with HTTP requests and database. 3) The huge ecosystem provides a wealth of tools and libraries. 4) Active community and open source nature adapts them to new needs and technology trends.

PHP and Python are both high-level programming languages that are widely used in web development, data processing and automation tasks. 1.PHP is often used to build dynamic websites and content management systems, while Python is often used to build web frameworks and data science. 2.PHP uses echo to output content, Python uses print. 3. Both support object-oriented programming, but the syntax and keywords are different. 4. PHP supports weak type conversion, while Python is more stringent. 5. PHP performance optimization includes using OPcache and asynchronous programming, while Python uses cProfile and asynchronous programming.

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

PHP remains important in the modernization process because it supports a large number of websites and applications and adapts to development needs through frameworks. 1.PHP7 improves performance and introduces new features. 2. Modern frameworks such as Laravel, Symfony and CodeIgniter simplify development and improve code quality. 3. Performance optimization and best practices further improve application efficiency.

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.


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