Variables in PHP

In PHP, a variable is like a container that stores data (like numbers, text, or other values) so you can use it later in your code.

Variables make it easy to reuse and manage data in your program.

There are some rules that are keep in mind when you create an variable:

Rules are:

1) Start with a $ sign:

All variable names always start with a dollar sign ($).

Example: 

$name = 10;

$age = "hello";

 

2) Variable name must start with a character or underscore (_):

Valid: $name, $_age

Invalid: $1name, $#age

 

3) Variable never hold any spacial symbol:

Means you have use symbols like: !#$%^&*()_ in veriable.

Valid: $user_name, $age1

Invalid: $user-name, $age!

 

4) Variable names are case-sensitive:

$name and $Name are two different variables.

 

5) Do not use reserved keywords:

Avoid using PHP keywords like echo, if, else, etc., as variable names.

Invalid: $echo, $if

 

6)Use meaningful names:

Give variables descriptive names to make your code easier to understand.

Example: Use $firstName instead of $fn.

---

---

 

15+ interview questions about PHP variables with answers and example

Question 1. What is a variable in PHP?

Answer: A variable in PHP is a container that stores data (like numbers, text, or other values) so it can be used later in the code.

Example:

$name = "John";
echo $name;

Output:

John

 

Question 2. How do you declare a variable in PHP?

Answer: In PHP, you declare a variable by starting with a $ sign, followed by the variable name and assigning a value to it.

Example:

$age = 25;

 

Question 3. What are the rules for naming variables in PHP?

Answer: The rules are:

• Start with a $ sign.
• Variable names must start with a letter or underscore (_).
• Can only contain letters, numbers, and underscores.
• Are case-sensitive.
• Cannot use reserved keywords (e.g., echo, if).

Example:

$firstName = "John"; // Valid
$first_name = "John"; // Valid
$1name = "John"; // Invalid

 

Question 4. What is a local variable in PHP?

Answer: A local variable is declared inside a block of code (like a function or loop) and can only be accessed within that block.

Example:

function test() {
    $localVar = "I am local";
    echo $localVar; 
}
test();
echo $localVar; 

Output:

I am local

Error: $localVar is not accessible outside the function

 

Question 5. What is a global variable in PHP?

Answer: A global variable is declared outside any block of code and can be accessed from anywhere in the script.

Example:

$globalVar = "I am global";
function test() {
    global $globalVar;
    echo $globalVar; 
}
test();
echo $globalVar;

Output:

I am global

I am global

 

Question 6. How do you access a global variable inside a function?

Answer: Use the global keyword to access a global variable inside a function.

Example:

$x = 10;
function test() {
    global $x;
    echo $x; 
}
test();

Output:

10

 

Question 7. Is PHP a dynamically typed language?

Answer: Yes, PHP is dynamically typed, meaning you don’t need to declare the type of a variable. The type is determined by the value assigned to it.

Example:

$x = 10;      // $x is an integer
$x = "Hello"; // Now $x is a string
echo $x; 

Output:

Hello

 

Question 8. Can a variable change its type in PHP?

Answer: Yes, a variable can change its type because PHP is dynamically typed.

Example:

$x = 10;      // $x is an integer
$x = "Hello"; // Now $x is a string
echo $x; 

Output:

Hello

 

Question 9. Are PHP variables case-sensitive?

Answer: Yes, PHP variables are case-sensitive. For example, $name and $Name are two different variables.

Example:

$name = "John";
$Name = "Doe";
echo $name; 
echo $Name; 

Output:

John
Doe

 

Question 10. What happens if you use a reserved keyword as a variable name?

Answer: PHP will throw an error because reserved keywords (like echo, if, else) cannot be used as variable names.

Example:

$echo = "Hello"; // Invalid

 

Question 11. What is variable interpolation in PHP?

Answer: Variable interpolation is the process of embedding variables directly inside double-quoted strings.

Example:

$name = "John";
echo "Hello, $name!";

Output:

Hello, John!

 

Question 12. Does variable interpolation work with single quotes?

Answer: No, variable interpolation only works with double quotes. Single quotes treat variables as plain text.

Example:

$name = "John";
echo 'Hello, $name!';

Output:

Hello, $name!

 

Question 13. What is a variable variable in PHP?

Answer: A variable variable allows you to use the value of one variable as the name of another variable.

Example:

$x = "name";
$$x = "John"; // Creates a variable $name with value "John"
echo $name; 

Output:

John

 

Question 14. What are predefined variables in PHP?

Answer: Predefined variables (also called superglobals) are built-in variables that are always available in all scopes. Examples include $_GET, $_POST, $_SESSION, and $_SERVER.

Example:

echo $_SERVER['PHP_SELF']; // Output: The current script's filename

 

Question 15. How do you destroy a variable in PHP?

Answer: Use the unset() function to destroy a variable.

Example:

$x = 10;
unset($x);
echo $x;

Output:

Error: $x is no longer defined