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PHP

properties

  • dynamically typed

  • weakly typed language

  • interpreted programming language

  • has garbage collection

  • doesn't have hoisted declarations

  • function-scoped variables

  • mutable strings

  • each statement must end with semicolon (;)

  • primarily used for web development

  • it is embedded in html

  • PHP is acronym for "Php: Hypertext Preprocessor"

  • uses .php file extension

basic syntax

php code is written between <?php and ?> (optional) tags:

<?php
echo "Hello, world!";
?>

Note

You don’t need to close the <?php tag in pure PHP files because: the PHP interpreter assumes the file ends with PHP code leaving it open avoids accidental whitespace or output after ?>, which can break things like headers or sessions

Feature echo print
Returns a value? ❌ No ✅ Yes (always 1)
Multiple arguments? ✅ Yes ❌ No
Performance ✅ Slightly better —
Usable in expressions ❌ No ✅ Yes

html + php integration example:

<!DOCTYPE html>
<html>
<head>
    <title>PHP Example</title>
</head>
<body>

    <h1>Welcome!</h1>

    <?php
        $name = "Alice";
        echo "<p>Hello, $name!</p>";
    ?>

</body>
</html>

generating html dynamically:

<ul>
<?php
$fruits = ["Apple", "Banana", "Cherry"];
foreach ($fruits as $fruit) {
    echo "<li>$fruit</li>";
}
?>
</ul>

data types

  • integer
  • float
  • boolean: case insensitive (e.g. both true and TRUE are valid)
  • string
  • array
  • object
  • null
  • resource: special data type to represent external resources (things that are not native php data types)
    • e.g. files, database connections

Important

all variable names must start with $

Warning

variable names can't start with a number or -

$age = 30;
$age++;
$price = 19.99;
$name = "Alice";
$isAdmin = true;
$isLoggedIn = false;

$colors = ["red", "green", "blue"];

$user = [
    "name" => "Alice",
    "age" => 30
];

$matrix = [
    [1, 2],
    [3, 4]
];

class Car {
    public $brand = "Toyota";
}

$car = new Car();
$middleName = null;
$file = fopen("example.txt", "r");

string operations

  • get string length: echo strlen("hello"); // 5

concatenate with .:

$name = "John";
$greeting = "Hello, " . $name; // "Hello, John"

string interpolation (requires double quotes):

$name = "Alice";
echo "Hi, $name!";  // Outputs: Hi, Alice!

get substring:

$str = "abcdef";
echo substr($str, 1, 3); // "bcd"

type checking

  • is_int()
  • is_string()
  • is_array()
  • is_object()
  • is_null()
  • is_bool()
$val = 42;
if (is_int($val)) {
    echo "It's an integer";
}

type casting

$val = "10";
$intVal = (int)$val;      // 10
$floatVal = (float)$val;  // 10.0
$boolVal = (bool)$val;    // true
$x = (string)100;         // "100"

if else

Warning

avoid and and or in expressions because both have lower precedence than =, which can lead to unexpected behaviour. use && and || instead use and and or in control flow (if, while, etc)

<?php
$grade = 85;

if ($grade >= 90) {
    echo "Excellent!";
} elseif ($grade >= 60) {
    echo "You passed.";
} else {
    echo "You failed.";
}
?>

loops

for ($i = 0; $i < 5; $i++) {
    echo $i;
}

$colors = ["red", "green", "blue"];
foreach ($colors as $color) {
    echo $color;
}

functions

function greet($name) {
    return "Hello, $name!";
}

echo greet("Alice");
  • range(3, 5);: returns array [3, 4, 5]
  • var_dump($var1): display info about 1 or more variables
  • sqrt($num)
  • pow($num)
  • round($num)
  • floor($num)
  • ceil($num)

classes and objects

use -> to access properties and methods of an object

class Person {
    public $name = "Alice";

    public function sayHello() {
        return "Hello, I'm $this->name";
    }
}

$p = new Person();
echo $p->name;           // Outputs: Alice
echo $p->sayHello();     // Outputs: Hello, I'm Alice

superglobals

special variables available anywhere

  • $_GET, $_POST: form data
  • $_SESSION, $_COOKIE: user/session data
  • $_SERVER: server environment
  • $_GLOBALS: superglobal associative array that stores all global variables
    • associative array: an array where keys are strings instead of numeric indexes
    • echo $GLOBALS['x']; // Access global variable $x
  • $_ENV: superglobal associative array in PHP that contains environment variables passed to the current script
    • echo $_ENV['APP_ENV']; // Output: production

connecting with a database

php + mysql

$host = "localhost";
$user = "root";
$password = "";
$dbname = "my_database";

$conn = new mysqli($host, $user, $password, $dbname);

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

run sql query:

$sql = "SELECT id, name FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // Loop through rows
    while ($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"] . " - Name: " . $row["name"] . "<br>";
    }
} else {
    echo "No results";
}

insert data:

$name = "Alice";
$sql = "INSERT INTO users (name) VALUES ('$name')";

if ($conn->query($sql) === TRUE) {
    echo "New record created";
} else {
    echo "Error: " . $conn->error;
}

use prepare statements to avoid sql injection:

$stmt = $conn->prepare("INSERT INTO users (name) VALUES (?)");
$stmt->bind_param("s", $name);
$stmt->execute();
  • closing the connecting: $conn->close();