PHP Reference

PHP Reference Guide

This PHP reference guide provides an overview of essential PHP functions, concepts, and syntax. It serves as a quick reference for common tasks and functionalities in PHP development.

1. PHP Syntax

Opening and Closing Tags:
```
<?php
// PHP code goes here
?>
```

Comments:

// Single-line comment
# Another single-line comment
/*
 Multi-line comment
*/

2. Variables

Declaration:
```
$variable_name = value;
```
Types:
- String: $name = "John";
- Integer: $age = 30;
- Float: $height = 5.9;
- Boolean: $is_student = true;

3. Data Types

Array:

$fruits = array("Apple", "Banana", "Cherry");

Associative Array:

$person = array("name" => "John", "age" => 30);

4. Control Structures

If...Else:

if ($condition) {
    // code to execute if condition is true
} elseif ($another_condition) {
    // code to execute if another_condition is true
} else {
    // code to execute if no conditions are true
}

Switch:

switch ($variable) {
    case 'value1':
        // code to execute
        break;
    default:
        // code to execute if no case matches
}

Loops:

For Loop:

for ($i = 0; $i < 10; $i++) {
    // code to execute
}

While Loop:

while ($condition) {
    // code to execute
}

5. Functions

Function Definition:

function functionName($parameter) {
    // code to execute
}

Returning Values:

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

6. Arrays

Accessing Elements:
```
$fruits[0]; // "Apple"
```

Looping Through Arrays:

foreach ($fruits as $fruit) {
    echo $fruit;
}

7. File Handling

Opening a File:
```
$file = fopen("filename.txt", "r");
```

Reading from a File:

$content = fread($file, filesize("filename.txt"));

Writing to a File:

$file = fopen("filename.txt", "w");
fwrite($file, "Hello, World!");

8. Sessions and Cookies

Starting a Session:

session_start();
$_SESSION['username'] = 'JohnDoe';

Setting a Cookie:

setcookie("user", "John", time() + (86400 * 30), "/");

9. Database Interaction

Connecting to MySQL:

$conn = new mysqli($servername, $username, $password, $dbname);

Executing a Query:

$result = $conn->query("SELECT * FROM users");

10. Common Functions

String Functions:
- strlen($string): Returns the length of a string.
- str_replace($search, $replace, $subject): Replaces all occurrences of a search string with a replacement string.
Array Functions:
- count($array): Returns the number of elements in an array.
- array_push($array, $value): Adds one or more elements to the end of an array.
Mathematical Functions:
- abs($number): Returns the absolute value of a number.
- round($number, $precision): Rounds a number to a specified precision.

Conclusion

This reference guide covers fundamental aspects of PHP, including syntax, control structures, functions, file handling, and database interactions. Use this guide as a quick reference while developing PHP applications. For more in-depth information, you can always refer to the official PHP documentation.

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