Common PHP Interview Questions for Developers

Understanding PHP Basics

What is PHP and why is it used?

PHP is a server-side scripting language designed for web development. It is used to create dynamic web pages and applications. A good answer should highlight PHP's ease of use, flexibility, and its ability to integrate with various databases.

Explain the difference between echo and print in PHP.

Both are used to output data to the screen. Echo can take multiple parameters, while print can only take one argument and always returns 1. A candidate should demonstrate understanding of these subtle differences.

PHP Syntax and Functions

How do you declare a variable in PHP?

Variables in PHP are declared with a dollar sign followed by the variable name. For example, $variableName. A good answer should include examples and mention PHP's dynamic typing.

What are PHP data types?

PHP supports several data types including integers, floats, strings, arrays, objects, and booleans. Candidates should be able to explain each type and provide examples.

How do you create a function in PHP?

Functions in PHP are created using the function keyword followed by the function name and parentheses. A good answer should include syntax and an example function.

Advanced PHP Concepts

What is the purpose of PHP's include and require statements?

Both are used to include files in PHP scripts. The difference is that require will produce a fatal error and stop the script if the file cannot be included, while include will only produce a warning. Candidates should explain when to use each.

Explain the concept of sessions in PHP.

Sessions are used to store data across multiple pages. They are useful for maintaining user state and data. A good answer should include how to start a session and how to store and retrieve session data.

What is an associative array in PHP?

An associative array uses named keys that you assign to them. This is different from a regular array that uses numeric keys. Candidates should provide examples and explain use cases.

PHP and Databases

How do you connect to a MySQL database using PHP?

Candidates should explain using the mysqli_connect function or PDO (PHP Data Objects) for database connections. A good answer should include error handling and security considerations like prepared statements.

What is SQL injection and how can you prevent it in PHP?

SQL injection is a code injection technique that might destroy your database. Candidates should explain how to prevent it using prepared statements and parameterized queries.

Object-Oriented PHP

What is object-oriented programming in PHP?

OOP is a programming style that uses objects and classes. Candidates should explain the concepts of classes, objects, inheritance, and polymorphism with examples.

How do you define a class in PHP?

A class is defined using the class keyword followed by the class name. A good answer should include syntax, properties, methods, and an example of instantiation.

Conclusion

These questions cover a range of topics from basic PHP syntax to advanced concepts like OOP and database interactions. Understanding these questions and their answers will help you assess a candidate's proficiency in PHP and their ability to apply this knowledge in real-world scenarios.