Variables & Data Types 📦

<?php
// A variable is a named box that holds a value.
// In PHP every variable name starts with a dollar sign ( $ ).

$name = "Alice";        // a string  — text in quotes
$age  = 28;             // an int    — a whole number
$price = 49.99;         // a float   — a number with a decimal point
$isMember = true;       // a bool    — only ever true or false
$nickname = null;       // null      — "no value yet"

// Inside DOUBLE quotes, PHP swaps a $variable for its value (interpolation).
echo "Name:  $name\n";
echo "Age:   $age\n";
echo "Price: $price\n";

// The = sign means "store this", NOT "is equal to".
$age = 29;              // overwrite the box: $age is now 29
echo "Next year: $age\n";
?>

Name:  Alice
Age:   28
Price: 49.99
Next year: 29

<?php
// PHP has 8 types. You'll use these 5 every day.
$title   = "PHP Basics";   // string  — text
$views   = 1500;           // int     — whole number
$rating  = 4.5;            // float   — decimal number
$isLive  = false;          // bool    — true / false
$author  = null;           // null    — deliberately empty

// var_dump() shows the TYPE and the value — your best debugging friend.
var_dump($title);
var_dump($views);
var_dump($rating);
var_dump($isLive);
var_dump($author);

// gettype() returns just the type name as a string.
echo gettype($views) . "\n";   // integer
echo gettype($rating) . "\n";  // double  (PHP calls floats "double")
?>

string(9) "PHP Basics"
int(1500)
float(4.5)
bool(false)
NULL
integer
double

<?php
// PHP is DYNAMICALLY typed: you never declare a type,
// and the same box can hold different types over time.
$data = "42";              // right now it's a string
echo gettype($data) . "\n";   // string

$data = 42;                // now the very same variable holds an int
echo gettype($data) . "\n";   // integer

$data = [1, 2, 3];         // now it's an array
echo gettype($data) . "\n";   // array

// This flexibility is handy — but it's why the == pitfalls below exist.
?>

string
integer
array

<?php
$name = "Sam";

// DOUBLE quotes interpolate: $name is replaced by its value.
echo "Hello, $name!\n";          // Hello, Sam!

// SINGLE quotes are literal: you get the text $name verbatim.
echo 'Hello, $name!' . "\n";     // Hello, $name!

// The dot ( . ) joins (concatenates) strings together.
$greeting = "Hi, " . $name . "!";
echo $greeting . "\n";           // Hi, Sam!

// Curly braces remove all doubt about where a variable name ends.
$item = "cup";
echo "I have two {$item}s.\n";   // I have two cups.
?>

Hello, Sam!
Hello, $name!
Hi, Sam!
I have two cups.

<?php
// 🎯 YOUR TURN — fill in each blank marked ___ , then run it.
// Each box should hold the right type for the value described.

$city  = ___;     // 👉 a string: your city in "double quotes"
$year  = ___;     // 👉 an int: a whole number like 2026
$score = ___;     // 👉 a float: a decimal like 9.5

echo gettype($city) . "\n";    // should print: string
echo gettype($year) . "\n";    // should print: integer
echo gettype($score) . "\n";   // should print: double

// ✅ Expected output:
//    string
//    integer
//    double
?>

string
integer
double

<?php
// 🎯 YOUR TURN — pick the RIGHT quotes so $name is interpolated.
$name = "Sam";

// 1) Make this print:  Hi, Sam!   (the value, not the text $name)
echo ___Hi, $name!___ . "\n";   // 👉 wrap the text in DOUBLE quotes

// 2) Join two strings with the dot operator into one greeting.
echo "Welcome " ___ $name . "!\n";   // 👉 replace ___ with a dot  .

// ✅ Expected output:
//    Hi, Sam!
//    Welcome Sam!
?>

Hi, Sam!
Welcome Sam!

<?php
// == compares VALUES after juggling types (loose).
// === compares value AND type (strict). Prefer === almost always.

var_dump(5 == "5");      // true  — "5" is juggled to the int 5
var_dump(5 === "5");     // false — int vs string, so strict fails

var_dump(0 == "");       // false — modern PHP (8+); was a classic trap before
var_dump("abc" == 0);    // false — non-numeric string is NOT juggled to 0 here

var_dump(1 === 1);       // true  — same value, same type
var_dump(null == false); // true  — both are "empty/falsy"
var_dump(null === false);// false — different types
?>

bool(true)
bool(false)
bool(false)
bool(false)
bool(true)
bool(true)
bool(false)

<?php
// A constant never changes once set. By convention it's UPPER_CASE
// and has NO dollar sign.

const MAX_USERS = 100;        // PHP-preferred, set at compile time
define('TAX_RATE', 0.20);     // older style, works at run time too

$subtotal = 50.00;
$total = $subtotal + ($subtotal * TAX_RATE);

echo "Tax rate: " . (TAX_RATE * 100) . "%\n";   // 20%
echo "Total:    $" . $total . "\n";             // 60
echo "Seat cap: " . MAX_USERS . "\n";           // 100

// MAX_USERS = 200;  // would be a fatal error — constants can't be reassigned.
?>

Tax rate: 20%
Total:    $60
Seat cap: 100

<?php
$name = "Ada";
$lang = "PHP";

// HEREDOC ( <<<"LABEL" ) acts like double quotes: it interpolates $variables.
$bio = <<<TEXT
Name: $name
Learns: $lang
TEXT;

// NOWDOC ( <<<'LABEL' ) acts like single quotes: everything is literal.
$raw = <<<'TEXT'
This $name is printed exactly as written.
TEXT;

echo $bio . "\n";
echo $raw . "\n";
?>

Name: Ada
Learns: PHP
This $name is printed exactly as written.