cheetsheetz/PHP.md

PHP Cheat Sheet

Table of Contents

1. Variables
2. Data Types
3. Operators
4. Control Structures
5. Functions
6. Arrays
7. Strings
8. File Handling
9. Error Handling
10. Classes and Objects
11. Sessions and Cookies
12. Database Connectivity
13. Regular Expressions

Variables

Declaration and Assignment

<?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

+, -, *, /, %, ** (exponentiation)

Comparison Operators

==, ===, !=, !==, <, >, <=, >=

Logical Operators

&& (and), || (or), ! (not)

Assignment Operators

=, +=, -=, *=, /=, %=

Control Structures

If Statement

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

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

for ($i = 0; $i < 5; $i++) {
    // code to be executed in each iteration
}

While Loop

while (condition) {
    // code to be executed as long as the condition is true
}

Do-While Loop

do {
    // code to be executed at least once, then repeated as long as the condition is true
} while (condition);

Functions

Function Declaration

function functionName($param1, $param2) {
    // code to be executed
    return $result; // optional
}

Function Call

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

Arrays

Indexed Array

$indexed_array = array("value1", "value2", "value3");

Associative Array

$assoc_array = array("key1" => "value1", "key2" => "value2");

Multidimensional Array

$multi_array = array(
    array("value1", "value2"),
    array("value3", "value4")
);

Strings

Concatenation

$string1 = "Hello";
$string2 = "World";
$concatenated = $string1 . " " . $string2;

String Functions

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

$file_content = file_get_contents("filename.txt");

Writing to a File

file_put_contents("filename.txt", "Hello, World!");

Error Handling

Try-Catch Block

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

Classes and Objects

Class Declaration

class MyClass {
    // properties and methods
}

Object Instantiation

$object = new MyClass();

Sessions and Cookies

Sessions

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

Cookies

setcookie('user', 'Jane', time() + 3600, '/');

Database Connectivity

MySQLi Connection

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

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

MySQLi Query

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

Regular Expressions

Pattern Matching

$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
$colors = array("Red", "Green", "Blue");

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

Switch Statement with Fall-Through

<?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
function greet($name = "Guest") {
    echo "Hello, " . $name . "!";
}

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

Variable Number of Arguments

<?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
$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
$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
// 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
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
$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();
?>