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🟢 Basic Level

1️⃣ What is a function in PHP?

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

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2️⃣ How do you define a function in PHP?

function myFunction() {
    echo "Hello";
}

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3️⃣ What is the difference between echo and return?

👉 echo → outputs directly
👉 return → sends value back to caller

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4️⃣ What are function parameters?

👉 Variables passed into a function as input.

function add($a, $b) {
    return $a + $b;
}

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5️⃣ What are default arguments?

👉 Predefined values used if no argument is passed.

function greet($name = "Guest") {
    echo $name;
}

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🟡 Intermediate Level

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6️⃣ What is the difference between pass by value and pass by reference?

👉 Pass by value (default):

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

👉 Pass by reference:

function test(&$x) {
    $x = 10;
}

📌 & allows modifying original variable

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7️⃣ What are variable functions in PHP?

👉 Calling functions using a variable name.

function hello() {
    echo "Hi";
}$f = "hello";
$f();

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8️⃣ What is a recursive function?

👉 A function that calls itself.

function countDown($n) {
    if ($n <= 0) return;
    echo $n;
    countDown($n - 1);
}

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9️⃣ What are built-in functions?

👉 Predefined PHP functions like:

• strlen()
• count()
• array_merge()

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🔟 What is function overloading in PHP?

👉 PHP does NOT support traditional function overloading.

But you can simulate it using:

• Default arguments
• func_get_args()

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🔴 Advanced Level

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1️⃣1️⃣ What are anonymous functions (closures)?

👉 Functions without name.

$greet = function($name) {
    return "Hello $name";
};echo $greet("Aditya");

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1️⃣2️⃣ What is a closure in PHP?

👉 Anonymous function that can access variables from outside using use.

$message = "Hello";$func = function() use ($message) {
    echo $message;
};$func();

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1️⃣3️⃣ What are arrow functions in PHP?

👉 Short syntax (PHP 7.4+)

$sum = fn($a, $b) => $a + $b;

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1️⃣4️⃣ What is callable in PHP?

👉 A type that represents valid function calls.

function run(callable $func) {
    $func();
}

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1️⃣5️⃣ What is function_exists()?

👉 Checks if function is defined.

if (function_exists('test')) {
    test();
}

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1️⃣6️⃣ What is include vs require in functions?

👉 include → warning if file missing
👉 require → fatal error (script stops)

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1️⃣7️⃣ Can a function return multiple values?

👉 Yes (using arrays)

function getData() {
    return [1, 2];
}

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1️⃣8️⃣ What are variable scope types in functions?

👉 Types:

• Local
• Global
• Static

function test() {
    static $x = 0;
    $x++;
    echo $x;
}

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1️⃣9️⃣ What is recursion base case?

👉 Condition to stop recursion.

if ($n == 0) return 1;

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2️⃣0️⃣ What is the use of global keyword?

👉 Access global variables inside function.

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

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🎯 Pro Interview Tips

👉 Interviewers often ask:

• Difference between echo vs return
• Pass by reference (&)
• Closures & arrow functions
• Recursion logic
• Scope (global/static)

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🚀 Bonus Coding Questions

Try solving:

1. Write a function to reverse a string
2. Create a function to find factorial (recursive)
3. Function to check palindrome
4. Pass array to function and return sum
5. Create a closure example
6. Dynamic calculator using variable functions