Core PHP Interview Questions

PHP stands for Hypertext Preprocessor.

PHP is a server-side scripting language used to create dynamic web pages. (server side means is It runs on the server not in the browser)

Execution

PHP → Server-Side Language

• PHP runs on the web server

• The browser receives only the final HTML output

• Users cannot see PHP code

• PHP is used for Database operations, Authentication (login systems), Sessions & cookies, REST API development

 Browser → Request → Server → PHP executes → HTML sent to browser 

JavaScript → Client-Side Language

• JavaScript runs in the browser

• It directly manipulates the DOM

• Code is visible to the user

• JavaScript is used for Handling button clicks & events, Form validation (without page reload), Animations, DOM manipulation

 Browser → JS executes → UI updates dynamically 

Interview line:
PHP is a server-side scripting language, while JavaScript is primarily a client-side scripting language.

A variable in PHP is a container used to store data (value), such as:

• numbers, strings, arrays, objects, boolean values

The value of a variable can change during program execution.

Note: In PHP, a variable always starts with $ (eg : $a = 10; or $name = "abc";)

A data type defines the type of value a variable can store.

Since PHP is a loosely typed language, you don’t need to declare the data type manually. PHP automatically detects it.

Types of Data Types in PHP:

1. Scalar Data Types (String, Integer, Float, Boolean)
2. Compound Data Types (Array,Object)
3. Special Data Types (NULL)

Both echo and print are used to display output in PHP.

Interview-Ready Answer :

echo and print are PHP language constructs used to display output. echo does not return any value and supports multiple parameters, making it slightly faster, while print returns 1 and can be used in expressions but accepts only one argument.

= : (Assignment operator) Assigns value to a variable

== : (Loose comparison) Compares value only (type conversion allowed)

=== : (Strict comparison) Compares value + data type

Interview-Ready Answer : 

= is an assignment operator, == compares only values with type conversion, and === compares both value and data type without conversion.

A constant is a name that holds a fixed value which cannot be changed once it is defined.

example : define("SITE_NAME", "InterviewReady");
                 echo SITE_NAME;

Difference Between Variable and Constant-

Variable : $name = "Mayank" (value can be change)

Constant : define("NAME", "Mayank") (value cannot be change)

1. for Loop : 

Used when you know how many times the loop should run.

for (initialization; condition; increment/decrement) {
    // code
}

//////////////////////////////////////

for ($i = 1; $i <= 5; $i++) {
    echo $i;
}

2. while Loop : 

Runs as long as the condition is true.

while (condition) {
    // code
}

//////////////////////////

$i = 1;

while ($i <= 5) {
    echo $i;
    $i++;
}

3. foreach Loop :

foreach ($array as $value) {
    // code
}

////////////////////////////

$colors = ["red", "green", "blue"];

foreach ($colors as $color) {
    echo $color;
}

A switch statement is used to execute different blocks of code based on different values of a variable.

It is an alternative to multiple if...elseif...else conditions.

switch (variable) {
    case value1:
        // code
        break;

    case value2:
        // code
        break;

    default:
        // code if no case matches
}

break-

The break statement is used to terminate the loop or switch immediately.

👉 It stops execution and comes out of the loop.

for ($i = 1; $i <= 5; $i++) {
    if ($i == 3) {
        break;
    }
    echo $i;
}

/////////////////////
output :
12

- Loop stops when $i == 3

continue-

The continue statement is used to skip the current iteration and move to the next iteration of the loop.

1. Loop does NOT stop 
2. Only skips one cycle

for ($i = 1; $i <= 5; $i++) {
    if ($i == 3) {
        continue;
    }
    echo $i;
}

/////////////////////

Output :
1245
Note : 3 is skipped but loop continues

What is a Function?

A function is a block of reusable code that performs a specific task.

Types of Functions in PHP

• Built-in functions (predefined by PHP)

• User-defined functions (created by the developer)

Built-in Functions :  

These are predefined functions provided by PHP. You don’t need to create them. (eg. strlen(), count(), date() etc.)

User-Defined Functions :

These are functions created by the programmer to perform custom tasks. (eg. function functionName() {// code} )

$_GET and $_POST are superglobal arrays in PHP used to collect form data.

They are used to send data from the client (browser) to the server.

$_POST -

$_POST is used to collect data sent using the HTTP POST method. 

important . Data is sent in the request body, not in the URL.

$_GET -

$_GET is used to collect data sent using the HTTP GET method.

Important : Data is sent through the URL

$_POST is a superglobal array that contains data sent using the HTTP POST method.

• Data comes only from POST
• Used for form submissions
• More secure than GET/REQUEST
• Data is sent in the request body (not visible in URL)

  $name = $_POST['name'];

$_REQUEST is a superglobal array that contains data from:

$_GET + $_POST + $_COOKIE

$name = $_REQUEST['name'];

it may come from: URL, Form, Cookie

MySQLi (MySQL Improved) is a PHP extension used to connect only with MySQL databases.

It supports:

• OOP style
• Procedural style
• Prepared statements

PDO (PHP Data Objects) is a database-independent extension.

It supports multiple databases:

• MySQL
• PostgreSQL
• SQLite
• Oracle
• SQL Server