How to write good PHP code?

Writing good code is an art. If a programmer follows some good programming habits, then he can become an excellent programmer. In fact, you will probably spend more time maintaining the code than you do writing the code; not to mention maintaining the entire application. Establishing good coding habits will improve design factors like modularity, and your code will be easier to understand and, therefore, easier and cheaper to maintain. And bad coding habits will leave flaws in the code and may make the code difficult to maintain.
In this article, we will explore some good programming practices that will help you avoid defects in your code.
1- Write modular code
Good PHP code should be modular code. PHP's object-oriented programming features are particularly powerful tools for breaking your application into functions or methods. You should separate as much as possible the front-end HTML/CSS/JavaScript code from the server-side of your application. You can also follow the MVC (Model-View-Controller) pattern on any PHP framework.
2- Code Writing Standards
Good PHP code should have a complete set of coding standards. Achieving programming standards through naming variables and functions, unified methods for accessing the database and handling errors, and the same code indentation method can make your code more readable.
3- Write Portable Code
Good PHP code should be portable. You can use PHP's existing features like magic quotes and short tags. Try to understand your needs and then write code to make it self-contained and portable by adapting PHP features.
4- Write secure code
Good PHP code should be secure. PHP5 provides excellent performance and flexibility. But the security issue lies entirely with the developers. For a professional PHP developer, it is crucial to have a deep understanding of major security vulnerabilities, such as: Cross-site scripting (XSS), Cross-site request forgery (CSRF), code injection vulnerabilities, and character encoding vulnerabilities. By using PHP's special features and functions, such as: mysql_real_escape_string, etc., you can write safe code.
5- Code Comments
Code comments are an important part of the code. Through code comments, you can know what the variable or function does, which will be very useful in future code maintenance.
6- Avoid short tags
Replace all short tags with complete PHP tags.
7- Use single quotes instead of double quotes
Always use single quotes instead of double quotes for strings to avoid performance degradation caused by PHP searching for variables within the string.
8- Escaped string output
It is a good practice to use ENT_QUOTES as a parameter to pass to the htmlspecialchars function to ensure that single quotes (') are also converted into HTML entities.
9- Use comma-separated string output
Outputting a string separated by commas (,) through the echo statement has better performance than using the string concatenation operator (.).
10- Check the passed value before outputting

Check the passed value $_GET['query'] before outputting. Using the isset or empty function, you can check whether a variable is null.

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