Server-side

PHP Expressions & Basics

Variable Naming

Use $ to declare variables.
Variables are case-sensitive.
Variable names must start with a letter or an underscore (_).

Strings

Double Quotes (" "): Variables inside double quotes expand.
Single Quotes (' '): Variables inside single quotes do not expand.

$name = "John";
echo "Hello, $name!";  // Output: Hello, John!
echo 'Hello, $name!';  // Output: Hello, $name!

Variables & Scope

Static Variables

If you want to retain a variable’s value after a function exits, use static:

function counter() {
    static $count = 0;
    $count++;
    echo $count . "\n";
}
counter(); // 1
counter(); // 2
counter(); // 3

Global Scope

A variable declared outside a function has global scope and can only be accessed outside a function.

Global Keyword

The global keyword allows access to a global variable inside a function.

$x = 5;
$y = 10;

function myTest() {
    global $x, $y;
    $y = $x + $y;
}

myTest();
echo $y; // Output: 15

Alternatively, use $GLOBALS:

$x = 5;
$y = 10;

function myTest() {
    $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}

myTest();
echo $y; // Output: 15

Local Scope

A variable declared inside a function is local to that function.

function myFunction() {
    $x = 10;
    echo $x;
}
myFunction();
// echo $x; // Error! $x is not accessible here.

Comments

Single-line comments: // or #
HTML comment:

Increment/Decrement Operators

$x = 12;
$y = 15 + $x++;
echo "x is $x and y is $y \n"; // x is 13 and y is 27

++$x (pre-increment): Increments first, then uses the value.
$x++ (post-increment): Uses the value first, then increments.

String Concatenation

$a = 'Hello ' . 'World';
echo $a; // Hello World

Ternary Operator

$www = 123;
$msg = $www > 100 ? "Large" : "Small"; // condition ? True : False
echo $msg; // Large

Side Effect Operator (`.=`)

$out = "Hello";
$out .= " World";
echo $out; // Hello World

Useful for growing strings efficiently.

Type Casting

+ (math operator) converts values to numbers.
. (string operator) converts values to strings.

$value = "same" + 25; // 25 ("same" is treated as 0)

Explicit casting:

$value = (int) 9.9 + 10; // 19

Boolean conversion examples:

echo "A" . FALSE . "B"; // AB
echo "A" . TRUE . "B";  // A1B

Comparison Operators

Equality (`==`)

Compares values without considering data types.

Identity (`===`)

Compares values with data type checking.

Caution:

FALSE is treated as 0, so functions returning 0 may be misinterpreted as FALSE.
Always check function return values carefully.

Control Structures

Conditional Statements

$ans = 42;
if ($ans == 42) {
    echo "Correct";
} elseif ($ans == 52) {
    echo "It's 52";
} else {
    echo "Wrong";
}

Shortened syntax:

$ans = 42;
if ($ans == 42) echo "Correct";
elseif ($ans == 52) echo "It's 52";
else echo "Wrong";

Switch case

its only check for equals only its difficult to check greater than or less than.

$favcolor = "red";
switch ($favcolor) {
  case "red":
    echo "Your favorite color is red!";
    break;
  case "blue":
    echo "Your favorite color is blue!";
    break;
  default:
    echo "Your favorite color is neither red",
}

we need to use break for stop evaluating other conditions. default use as a if no similar cases

Loops

While Loop

$fuel = 10;
while ($fuel > 1) {
    echo "Broom broom";
    $fuel = $fuel - 1;
}

Do-While Loop

$fuel = 10;
do {
    echo "Broom broom";
    $fuel = $fuel - 1;
} while ($fuel > 1);

For Loop

for ($i = 0; $i < 5; $i++) {
    echo "Iteration: $i\n";
}

Foreach Loop

foreach($colors as $value){
  echo "color :" . $value
}

Loop Control

Use break to exit a loop completely.
Use continue to skip the current iteration and proceed to the next one.

Arrays

Key-Value Pair

$stuff = array("name" => "John", "course" => "CS50");

Creating an Empty Array and Appending Values

$va = array();
$va[] = "Hello"; // Array([0] => "Hello")

$vaa = array();
$vaa["name"] = "John"; // Array(["name"] => "John")

Looping Through an Array

$stuff = array("name" => "John", "course" => "CS50");

foreach($stuff as $key => $value){
    echo "Key: " . $key . " Value: " . $value . "\n";
}

Indexed Array Loop

$stuff = array("John", "Michel");

for($i = 0; $i < count($stuff); $i++){
    echo "Index: " . $i . " Value: " . $stuff[$i] . "\n";
}

Multi-dimensional Arrays

$product = array(
    'paper' => array(
        'copier' => 'copier and multipurpose'
    )
);

echo $product['paper']['copier']; // copier and multipurpose

Null Coalescing Operator

$stuff = array("name" => "John", "course" => "CS50");

$name = $stuff['name'] ?? 'not found'; // PHP 7+

Equivalent to:

$name = isset($stuff['name']) ? $stuff['name'] : 'not found';

Sorting Arrays

Sort by Values

$values = array("b" => 3, "a" => 1, "c" => 2);
asort($values); // Sorts by values

Sort by Keys

ksort($values); // Sorts by keys

Sort (Loses Keys)

sort($values); // Drops key-value association

Functions

Call by Value

function greet($name = "world") {
    return "Hello " . $name;
}
echo greet(); // Hello world

Call by Reference

function greet(&$name) {
    $name = "Alice";
}
$person = "John";
greet($person);
echo $person; // Alice

Modularity

include / include_once
require / require_once

MySQL

PDO (PHP Data Objects) - preferred
MySQLi (MySQL Improved)

Forms

Each form input must have a unique name attribute.

Sessions

super global variable isset : check variable declared or not

session_start();