PHP is a server-side scripting language used to create dynamic web applications. Understanding PHP’s syntax and variables is fundamental for writing efficient scripts.
1. Basic PHP Syntax
1.1 PHP Script Structure
A PHP script is enclosed within <?php … ?> tags. The PHP code inside these tags is executed on the server, and the output is sent as HTML to the browser.
<?php
echo “Hello, World!”;
?>
1.2 PHP File Extension
- PHP files are saved with the .php extension (e.g., index.php).
- A PHP file can contain PHP code, HTML, JavaScript, and CSS.
1.3 Embedding PHP in HTML
PHP can be written inside HTML to create dynamic pages.
<!DOCTYPE html>
<html>
<head>
<title>PHP Syntax Example</title>
</head>
<body>
<h1><?php echo “Welcome to My Website”; ?></h1>
</body>
</html>
- The <?php echo “text”; ?> syntax outputs text inside HTML.
2. PHP Statements and Comments
2.1 Ending PHP Statements
- Every PHP statement must end with a semicolon (;).
<?php
echo “Hello, World!”; // Correct
?>
2.2 PHP Comments
PHP supports single-line and multi-line comments.
<?php
// Single-line comment
echo “Hello, PHP!”;
# Another single-line comment
/*
Multi-line comment
This comment spans multiple lines
*/
?>
- Comments are ignored by the PHP interpreter and are used for documentation.
3. Variables in PHP
3.1 What is a Variable?
A variable in PHP is used to store data (strings, numbers, arrays, etc.). Variables start with a dollar sign ($) and are case-sensitive.
<?php
$name = “John”;
$age = 25;
echo “My name is ” . $name . ” and I am ” . $age . ” years old.”;
?>
Output:
My name is John and I am 25 years old.
3.2 Rules for Naming Variables
- Must start with a $ sign ($name).
- Must begin with a letter or underscore ($var1, $_var).
- Cannot contain spaces ($user_name instead of $user name).
- Case-sensitive ($var is different from $Var).
4. Variable Types in PHP
PHP is a loosely typed language, meaning variables do not need to be declared with a type.
4.1 String Variables
A string stores text and must be enclosed in single (”) or double (“”) quotes.
<?php
$str1 = “Hello, World!”;
$str2 = ‘PHP is awesome!’;
echo $str1 . ” ” . $str2;
?>
- Double-quoted strings allow variable interpolation (“Hello, $name” will replace $name with its value).
- Single-quoted strings do not allow interpolation (‘Hello, $name’ will output $name as text).
4.2 Integer Variables
An integer is a whole number (positive or negative).
<?php
$x = 100;
$y = -50;
echo $x + $y; // Output: 50
?>
4.3 Float (Decimal) Variables
A float (or double) is a number with a decimal point.
<?php
$price = 9.99;
echo “The price is $” . $price;
?>
4.4 Boolean Variables
A boolean can only have two values: true or false.
<?php
$is_logged_in = true;
echo $is_logged_in; // Output: 1 (true is displayed as 1)
?>
4.5 Array Variables
An array stores multiple values in a single variable.
<?php
$fruits = array(“Apple”, “Banana”, “Cherry”);
echo “I like ” . $fruits[0]; // Output: I like Apple
?>
4.6 Null Variables
A null variable has no value.
<?php
$x = null;
echo $x; // Output: (empty)
?>
5. Variable Scope in PHP
Variable scope defines where a variable can be accessed.
5.1 Local Scope
Variables declared inside a function are local and cannot be used outside.
<?php
function myFunction() {
$num = 10; // Local variable
echo $num;
}
myFunction();
echo $num; // Error: Undefined variable
?>
5.2 Global Scope
Variables declared outside functions are global but cannot be accessed inside functions directly.
<?php
$message = “Hello, World!”; // Global variable
function displayMessage() {
global $message; // Access global variable
echo $message;
}
displayMessage(); // Output: Hello, World!
?>
5.3 Static Variables
Static variables retain their value across function calls.
<?php
function counter() {
static $count = 0;
$count++;
echo $count;
}
counter(); // Output: 1
counter(); // Output: 2
?>
6. Variable Manipulation in PHP
6.1 Checking Variable Type
PHP provides functions to check a variable’s type.
<?php
$num = 10;
echo gettype($num); // Output: integer
?>
6.2 Type Casting
You can convert a variable’s type.
<?php
$x = “100”;
$y = (int) $x; // Cast string to integer
echo gettype($y); // Output: integer
?>
6.3 isset() and empty() Functions
- isset($var): Checks if a variable is set and not null.
- empty($var): Checks if a variable is empty (0, null, false, “”).
<?php
$var1 = “Hello”;
$var2 = “”;
echo isset($var1); // Output: 1 (true)
echo empty($var2); // Output: 1 (true)
?>
7. Conclusion
- PHP variables store different data types and are loosely typed.
- PHP supports local, global, and static variable scopes.
- Using isset() and empty() helps check variable values.
- Understanding PHP syntax and variables is essential for dynamic web development.