7 questions foundWhat is PHP and what makes it particularly well suited for web development?
Beginner PHP is a widely used, open source scripting language designed specifically for web development, letting you embed code directly within HTML pages or run it as standalone scripts, and it is well suited for the web because it runs on the server before a page is sent to the browser, integrates easily with databases, and is supported by virtually every web hosting provider, making it a practical and accessible choice for building dynamic websites.
<?php
echo "Hello, World!";
?>
Real-world example A small business builds its website using PHP to dynamically display product information pulled from a database, generating a fresh page for each visitor rather than relying on static, unchanging HTML files.
Common follow-ups: What is the difference between a scripting language and a compiled language?;Which popular websites and platforms are built using PHP?
OOP;PDO & Databases
What are the basic data types available in PHP?
Beginner PHP supports several basic data types including integers for whole numbers, floats for decimal numbers, strings for text, booleans for true or false values, arrays for collections of values, and a few special types like null representing no value at all, and object for instances of classes, with PHP automatically determining a variable's type based on the value assigned to it rather than requiring you to explicitly declare it upfront.
$age = 30;
$price = 19.99;
$name = "Ali";
$isActive = true;
Real-world example A user registration form stores the user's age as an integer, their account balance as a float, and their username as a string, with PHP automatically handling each variable according to its assigned type.
Common follow-ups: What is the difference between an integer and a float in terms of how PHP stores them?;How do you check the type of a specific variable?
Type Declarations & Strict Types;Arrays in PHP
What is type juggling in PHP, and how does it affect comparisons between values of different types?
Intermediate Type juggling refers to PHP's automatic conversion of a value from one type to another based on the context it is used in, such as automatically converting a string containing digits into a number when used in a mathematical operation, and this behavior significantly affects comparisons, since using the loose equality operator can produce surprising results, like the string zero being considered equal to false, which is why PHP also provides a strict equality operator that compares both value and type together.
var_dump("5" == 5);
var_dump("5" === 5);
var_dump(0 == "abc");
Real-world example A developer debugging an unexpected login bypass discovers that a loose comparison between a user submitted string and a stored value was allowing certain unintended matches due to type juggling, and switches the comparison to use the strict equality operator to fix it.
Common follow-ups: Why does PHP evaluate the string zero as equal to false using loose comparison?;What is the recommended best practice regarding loose versus strict comparison?
Type Declarations & Strict Types;Security
How do variable variables and variable scope work in PHP, and what are common pitfalls to avoid?
Intermediate A variable variable lets you use the value of one variable as the name of another variable, referenced using a double dollar sign syntax, which can be useful in specific dynamic scenarios but is generally discouraged for typical code since it makes programs significantly harder to read and debug, while variable scope determines where in your code a variable is accessible, with variables declared inside a function generally being local to that function unless explicitly passed in or declared as global.
$fieldName = 'email';
$$fieldName = 'user@example.com';
echo $email;
Real-world example A framework's internal templating engine occasionally uses variable variables to dynamically populate template placeholders, though most application level code deliberately avoids this pattern in favor of more explicit, readable approaches like arrays.
Common follow-ups: Why are variable variables generally considered a code smell in typical application code?;How does using the global keyword inside a function affect variable scope?
Functions & Scope;Constants & Superglobals
What are PHP's comparison operators, and how does the spaceship operator introduced in PHP 7 simplify writing custom comparison logic?
Intermediate PHP provides standard comparison operators like equal to, not equal to, greater than, and less than, along with the spaceship operator, which compares two values and returns negative one, zero, or one depending on whether the first value is less than, equal to, or greater than the second, making it especially convenient for writing concise custom sorting logic within functions like usort.
$result = 5 <=> 3;
echo $result;
usort($numbers, fn($a, $b) => $a <=> $b);
Real-world example A sorting function for a leaderboard uses the spaceship operator within a custom comparison callback to sort players by score, expressing the comparison logic in a single, clear line rather than a multi line if else structure.
Common follow-ups: What does the spaceship operator return for equal values?;How does the spaceship operator behave when comparing arrays or objects?
Arrays in PHP;Functions & Scope
How do PHP's integer and float types handle precision limitations, and what issues can arise when performing arithmetic with floating point numbers?
Advanced PHP floats are stored using standard floating point representation, which cannot always represent decimal fractions exactly, meaning arithmetic operations on floats, such as adding certain decimal values together, can produce results with tiny rounding errors that are not immediately visible but can cause subtle bugs, particularly in financial calculations, which is why many applications instead use integer based representations, such as storing currency amounts in cents, or a dedicated arbitrary precision library for money related calculations.
var_dump(0.1 + 0.2 == 0.3);
// This may output false due to floating point precision
$cents = 1050; // representing $10.50 as an integer to avoid precision issues
Real-world example A financial application avoids storing prices as floats entirely, instead storing every monetary value as an integer number of cents, completely sidestepping floating point precision issues that could otherwise cause subtle discrepancies in calculated totals.
Common follow-ups: What is the BCMath extension and how does it help with precise arithmetic?;Why is floating point precision loss considered especially dangerous in financial applications?
Type Declarations & Strict Types;PDO & Databases
How does PHP's type coercion behave differently in strict types mode compared to the default coercive mode, and what are the implications for function argument and return type validation?
Advanced In PHP's default coercive typing mode, scalar type declarations on function parameters and return values are automatically converted where possible, such as a string containing digits being silently converted to an integer, while declaring strict_types at the very top of a file disables this automatic coercion for that specific file, meaning a mismatched type passed into a strictly typed function throws a TypeError immediately rather than being silently converted, catching potential bugs much earlier in the development process.
declare(strict_types=1);
function addNumbers(int $a, int $b): int {
return $a + $b;
}
addNumbers("5", 3); // Throws TypeError under strict_types
Real-world example A team adopts strict_types across their entire codebase after discovering that a silently coerced string value had caused an incorrect calculation deep within their billing system, catching similar issues immediately as TypeErrors going forward instead of producing subtly wrong results.
Common follow-ups: Does declare(strict_types=1) affect the entire application or just the specific file it appears in?;How does strict typing interact with nullable type declarations?
Type Declarations & Strict Types;Error & Exception Handling