# PHP Cheat Sheet

## Table of Contents

1. [Variables](#variables)
2. [Data Types](#data-types)
3. [Operators](#operators)
4. [Control Structures](#control-structures)
5. [Functions](#functions)
6. [Arrays](#arrays)
7. [Strings](#strings)
8. [File Handling](#file-handling)
9. [Error Handling](#error-handling)
10. [Classes and Objects](#classes-and-objects)
11. [Sessions and Cookies](#sessions-and-cookies)
12. [Database Connectivity](#database-connectivity)
13. [Regular Expressions](#regular-expressions)

## Variables

### Declaration and Assignment
```php
<?php
$variable_name = value;
?>
```

### Variable Types
- String: `$string_variable = "Hello";`
- Integer: `$int_variable = 42;`
- Float: `$float_variable = 3.14;`
- Boolean: `$bool_variable = true;`

## Data Types

### Scalar Types
- String
- Integer
- Float (double)
- Boolean

### Compound Types
- Array
- Object

### Special Types
- Resource
- NULL

## Operators

### Arithmetic Operators
```php
+, -, *, /, %, ** (exponentiation)
```

### Comparison Operators
```php
==, ===, !=, !==, <, >, <=, >=
```

### Logical Operators
```php
&& (and), || (or), ! (not)
```

### Assignment Operators
```php
=, +=, -=, *=, /=, %=
```

## Control Structures

### If Statement
```php
if (condition) {
    // code to be executed if the condition is true
} elseif (another_condition) {
    // code to be executed if the previous condition was false and this one is true
} else {
    // code to be executed if all conditions are false
}
```

### Switch Statement
```php
switch (variable) {
    case value1:
        // code to be executed if variable equals value1
        break;
    case value2:
        // code to be executed if variable equals value2
        break;
    default:
        // code to be executed if variable doesn't match any case
}
```

### Loops
#### For Loop
```php
for ($i = 0; $i < 5; $i++) {
    // code to be executed in each iteration
}
```

#### While Loop
```php
while (condition) {
    // code to be executed as long as the condition is true
}
```

#### Do-While Loop
```php
do {
    // code to be executed at least once, then repeated as long as the condition is true
} while (condition);
```

## Functions

### Function Declaration
```php
function functionName($param1, $param2) {
    // code to be executed
    return $result; // optional
}
```

### Function Call
```php
$result = functionName($arg1, $arg2);
```

## Arrays

### Indexed Array
```php
$indexed_array = array("value1", "value2", "value3");
```

### Associative Array
```php
$assoc_array = array("key1" => "value1", "key2" => "value2");
```

### Multidimensional Array
```php
$multi_array = array(
    array("value1", "value2"),
    array("value3", "value4")
);
```

## Strings

### Concatenation
```php
$string1 = "Hello";
$string2 = "World";
$concatenated = $string1 . " " . $string2;
```

### String Functions
```php
strlen($string);    // length of the string
strpos($string, "find");    // position of the first occurrence of "find"
substr($string, start, length);    // extract a portion of the string
```

## File Handling

### Reading from a File
```php
$file_content = file_get_contents("filename.txt");
```

### Writing to a File
```php
file_put_contents("filename.txt", "Hello, World!");
```

## Error Handling

### Try-Catch Block
```php
try {
    // code that may throw an exception
} catch (Exception $e) {
    // handle the exception
    echo "Error: " . $e->getMessage();
}
```

## Classes and Objects

### Class Declaration
```php
class MyClass {
    // properties and methods
}
```

### Object Instantiation
```php
$object = new MyClass();
```

## Sessions and Cookies

### Sessions
```php
session_start();
$_SESSION['username'] = 'John';
```

### Cookies
```php
setcookie('user', 'Jane', time() + 3600, '/');
```

## Database Connectivity

### MySQLi Connection
```php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

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

### MySQLi Query
```php
$sql = "SELECT * FROM table";
$result = $conn->query($sql);
```

## Regular Expressions

### Pattern Matching
```php
$pattern = "/[0-9]+/";
$string = "There are 123 apples";
preg_match($pattern, $string, $matches);
```

```
# PHP Extended Examples

## Variables

### Variable Scope
```php
<?php
$global_variable = "I am global";

function myFunction() {
    $local_variable = "I am local";
    echo $local_variable; // Accessible within the function
    echo $global_variable; // Accessing a global variable requires the global keyword
}

myFunction();
echo $global_variable; // Accessible outside the function
// echo $local_variable; // This will throw an error since $local_variable is not in scope
?>
```

## Control Structures

### Foreach Loop with Arrays
```php
<?php
$colors = array("Red", "Green", "Blue");

foreach ($colors as $color) {
    echo $color . "\n";
}
?>
```

### Switch Statement with Fall-Through
```php
<?php
$day = "Monday";

switch ($day) {
    case "Monday":
    case "Tuesday":
        echo "It's a weekday.";
        break;
    case "Saturday":
    case "Sunday":
        echo "It's the weekend.";
        break;
    default:
        echo "Not a valid day.";
}
?>
```

## Functions

### Default Parameter Values
```php
<?php
function greet($name = "Guest") {
    echo "Hello, " . $name . "!";
}

greet(); // Outputs: Hello, Guest!
greet("John"); // Outputs: Hello, John!
?>
```

### Variable Number of Arguments
```php
<?php
function sum(...$numbers) {
    $result = 0;
    foreach ($numbers as $number) {
        $result += $number;
    }
    return $result;
}

echo sum(1, 2, 3, 4); // Outputs: 10
?>
```

## Arrays

### Array Functions
```php
<?php
$numbers = array(1, 2, 3, 4, 5);

// Count elements in an array
echo count($numbers); // Outputs: 5

// Find the sum of array elements
echo array_sum($numbers); // Outputs: 15

// Merge two arrays
$moreNumbers = array(6, 7, 8);
$combined = array_merge($numbers, $moreNumbers);
print_r($combined); // Outputs: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 [6] => 7 [7] => 8 )
?>
```

## Strings

### Regular Expression Match and Replace
```php
<?php
$string = "The quick brown fox jumps over the lazy dog";

// Check if the string contains the word "fox"
if (preg_match("/fox/", $string)) {
    echo "Found a fox!";
}

// Replace "fox" with "cat"
$newString = preg_replace("/fox/", "cat", $string);
echo $newString; // Outputs: The quick brown cat jumps over the lazy dog
?>
```

## File Handling

### Reading and Writing to Files
```php
<?php
// Reading from a file
$file_content = file_get_contents("example.txt");
echo $file_content;

// Writing to a file
$new_content = "This is some new content.";
file_put_contents("example.txt", $new_content);
?>
```

## Classes and Objects

### Class Inheritance
```php
<?php
class Animal {
    public $name;

    public function __construct($name) {
        $this->name = $name;
    }

    public function makeSound() {
        echo "Generic animal sound\n";
    }
}

class Dog extends Animal {
    public function makeSound() {
        echo "Woof!\n";
    }
}

$dog = new Dog("Buddy");
echo $dog->name; // Outputs: Buddy
$dog->makeSound(); // Outputs: Woof!
?>
```

## Database Connectivity

### MySQLi Prepared Statements
```php
<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

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

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

// Prepared statement
$sql = "SELECT * FROM users WHERE username = ?";
$stmt = $conn->prepare($sql);
$username = "john_doe";
$stmt->bind_param("s", $username);
$stmt->execute();

// Fetch result
$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
    print_r($row);
}

// Close connection
$stmt->close();
$conn->close();
?>
```

```