What is a Function in PHP?

A function is a reusable block of code that performs a specific task, can accept parameters as input, and can return a value as output.

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Definition

A function in PHP is a self-contained module of code that:

• Groups a set of statements together to perform a particular task
• Can be called (invoked) multiple times from anywhere in the program
• Helps in code reusability, modularity, and readability
• Reduces code redundancy (avoids writing same code again and again)

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Types of Functions in PHP

• Built-in functions — Pre-defined functions provided by PHP (e.g., strlen(), array_push())
• User-defined functions — Functions created by the programmer as per requirement

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How to Define a Function in PHP

Syntax:

function functionName($parameter1, $parameter2) {
    // body of the function
    return $value;
}

Rules for defining a function:

• A function is defined using the keyword function
• Function name must start with a letter or underscore (not a number)
• Function names are case-insensitive
• Parameters are placed inside parentheses ()
• The return statement sends a value back to the caller

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How to Call a Function in PHP

A function is called by writing its name followed by parentheses with arguments (if any):

$result = functionName($arg1, $arg2);

• When a function is called, the control transfers to the function body
• After execution, the control returns back to the calling statement
• Arguments are the actual values passed during the function call

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PHP Program: Function with Parameters and Return Value

<?php
// Function definition with parameters and return value
function calculateArea($length, $width) {
    $area = $length * $width;
    return $area;
}

// Function call with arguments
$result = calculateArea(10, 5);
echo "Area of rectangle = " . $result;

// Another function with parameters and return value
function addNumbers($a, $b) {
    $sum = $a + $b;
    return $sum;
}

$total = addNumbers(25, 35);
echo "<br>Sum = " . $total;
?>

Output:

Area of rectangle = 50
Sum = 60

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Explanation of the Program

• calculateArea($length, $width) — A user-defined function that takes two parameters (length and width)
• Inside the function, it calculates the area and uses return to send the result back
• calculateArea(10, 5) — The function is called with arguments 10 and 5
• The returned value is stored in $result and displayed using echo

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Conclusion

Functions are fundamental building blocks in PHP that promote code reusability and modular programming. By using parameters, we pass data into functions, and by using return values, we get processed results back — making our code clean, organized, and efficient.