Day 9 PHP Function: Numeric, Built in, String, Date, User Defined

Day 9 PHP Function: Numeric, Built in, String, Date, User Defined

What is a Function? Why Use Functions?

A function in programming is a reusable block of code designed to perform a specific task. Functions are fundamental because they promote reusability, modularity, and cleaner code. In PHP, functions can accept inputs (arguments) and return outputs.

Why Use Functions?

1. Code Reusability: Write once and reuse across scripts.
2. Better Organization: Group logically related tasks together.
3. Dynamic Behavior: Perform operations on dynamic data.
4. Maintenance Ease: Update logic in one place instead of multiple locations.

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Types of PHP Functions

1. Built-in Functions

These are pre-defined functions in PHP, categorized as:

• String Functions: Manipulate text (e.g., strlen(), str_replace()).
• Numeric Functions: Perform numeric operations (e.g., abs(), round()).
• Date Functions: Handle date/time (e.g., date(), strtotime()).
• File Functions: Manage file handling (e.g., fopen(), file_get_contents()).
• Database Functions: Work with databases (e.g., mysqli_connect(), PDO).

Example of a built-in String Function:

php

<?php
echo strlen("Hello World!"); // Outputs 12
?>

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2. User-Defined Functions

These are custom functions created by developers to meet specific needs.

Key Rules for User-Defined Functions

• Must start with a letter or underscore (_), not a number.
• Should have unique names.
• Avoid spaces in names.
• Use descriptive names for clarity.

Examples

1. Basic Function:

php

<?php
function greet() {
    echo "Hello, World!";
}
greet(); // Outputs: Hello, World!
?>

2. Function with Parameters:

php

<?php
function add($num1, $num2) {
    return $num1 + $num2;
}
echo add(5, 10); // Outputs: 15
?>

3. Function with Default Parameters:

php

<?php
function welcome($name = "Guest") {
    echo "Welcome, " . $name;
}
welcome(); // Outputs: Welcome, Guest
welcome("Alice"); // Outputs: Welcome, Alice
?>

4. Function Returning a Value:

php

<?php
function multiply($a, $b) {
    return $a * $b;
}
$result = multiply(4, 5);
echo $result; // Outputs: 20
?>

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Built-in Date Functions in PHP

PHP provides a rich set of date and time functions. Here are some commonly used ones:

1. date(): Formats a local date/time.

php

<?php
echo date("Y-m-d H:i:s"); // Outputs: 2024-12-04 12:00:00
?>

2. strtotime(): Converts a textual date into a Unix timestamp.

php
<?php
$timestamp = strtotime("next Monday");
echo date("Y-m-d", $timestamp); // Outputs the next Monday's date
?>

3. date_diff(): Calculates the difference between two dates.

php

<?php
$date1 = date_create("2024-01-01");
$date2 = date_create("2024-12-31");
$diff = date_diff($date1, $date2);
echo $diff->format("%R%a days"); // Outputs: +365 days
?>

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Advantages of User-Defined Functions

1. Custom Logic: Address specific application requirements.
2. Reusable Code: Call the function across multiple scripts/pages.
3. Simplified Debugging: Isolate and test individual blocks of code.
4. Improved Readability: Enhance code structure with meaningful function names.

Example of Reusability in User-Defined Functions

php
<?php
function calculateDiscount($price, $discountPercent) {
    return $price - ($price * $discountPercent / 100);
}

echo calculateDiscount(1000, 10); // Outputs: 900
echo calculateDiscount(500, 20);  // Outputs: 400
?>

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Summary

• Functions simplify and optimize PHP coding.
• Built-in functions offer ready-to-use solutions for common tasks.
• User-defined functions enable flexibility for unique needs.
• Functions improve code organization, maintenance, and efficiency.