PHP Syntax

Learning the rules and structure of PHP code

📝 PHP Syntax Basics

PHP syntax defines how you write code. PHP scripts start with <?php and end with ?>. Statements end with semicolons. PHP is case-sensitive for variables but not for keywords. 


<?php
// Basic PHP syntax
echo "Hello World!";
?>

Output:

Hello World!

PHP Syntax Rules

🏷️

PHP Tags

PHP code must be enclosed in <?php and ?> tags. These tell the server where PHP code begins and ends in your file. 

<?php
echo "PHP code here";
?>
;

Semicolons

Every PHP statement must end with a semicolon (;). This tells PHP where one instruction ends and another begins. 

<?php
echo "Statement 1";
echo "Statement 2";
?>
Aa

Case Sensitivity

Variables are case-sensitive ($name ≠ $Name), but keywords and function names are not (ECHO = echo = Echo). 

<?php
$name = "John";
ECHO $name; // Works
?>
⎵

Whitespace

PHP ignores extra spaces, tabs, and line breaks. Use whitespace to make your code readable and organized. 

<?php
echo    "Hello"   ;
echo "World";
?>

🔹 PHP Opening and Closing Tags

Different ways to use PHP tags in your code:

🔸 Standard PHP Tags (Recommended) 


<?php
echo "This is the standard way";
?>

🔸 Short Echo Tags 


<!-- Useful for outputting variables in HTML -->
<p>Welcome, <?= $username ?></p>

<!-- Equivalent to: -->
<p>Welcome, <?php echo $username; ?></p>

🔸 PHP-Only Files 


<?php
// For files with only PHP code, omit closing tag
// This prevents accidental whitespace issues

echo "No closing tag needed";
// No ?> at the end

Best Practice: For pure PHP files (no HTML), omit the closing ?> tag to avoid whitespace problems.

🔹 PHP Statements

Understanding how to write PHP statements correctly: 


<?php
// Single statement
echo "Hello";

// Multiple statements
echo "First line";
echo "Second line";
echo "Third line";

// Statement spanning multiple lines (still needs one semicolon)
echo "This is a very long statement " .
     "that spans multiple lines " .
     "for better readability";

// Multiple statements on one line (not recommended)
echo "One"; echo "Two"; echo "Three";
?>

Output:

HelloFirst lineSecond lineThird lineThis is a very long statement that spans multiple lines for better readabilityOneTwoThree

🔹 Mixing PHP with HTML

PHP can be embedded anywhere in HTML documents: 


<!DOCTYPE html>
<html>
<head>
    <title><?php echo "Dynamic Title"; ?></title>
</head>
<body>
    <h1>Welcome to My Site</h1>
    
    <?php
    $username = "Alice";
    $loginTime = date("h:i A");
    ?>
    
    <p>Hello, <?php echo $username; ?>!</p>
    <p>You logged in at <?= $loginTime ?></p>
    
    <?php
    // More PHP code
    for ($i = 1; $i <= 3; $i++) {
        echo "<p>Item $i</p>";
    }
    ?>
</body>
</html>

Output:

Welcome to My Site

Hello, Alice!

You logged in at 02:30 PM

Item 1

Item 2

Item 3

🔹 Case Sensitivity Examples

Understanding what is and isn't case-sensitive in PHP: 


<?php
// Keywords are NOT case-sensitive
ECHO "Hello";
echo "Hello";
Echo "Hello";  // All work the same

// Function names are NOT case-sensitive
STRLEN("text");
strlen("text");
StrLen("text");  // All work the same

// Variables ARE case-sensitive
$name = "John";
$Name = "Jane";
$NAME = "Jack";

echo $name;  // Outputs: John
echo $Name;  // Outputs: Jane
echo $NAME;  // Outputs: Jack

// Class names are NOT case-sensitive
class MyClass {}
$obj1 = new MyClass();
$obj2 = new myclass();  // Works
$obj3 = new MYCLASS();  // Works
?>

Output:

HelloHelloHelloJohnJaneJack

🔹 PHP Output Methods

Different ways to display output in PHP:

🔸 echo Statement 


<?php
// echo can output multiple strings
echo "Hello", " ", "World!";

// echo with concatenation
echo "Hello" . " " . "World!";

// echo without parentheses (common)
echo "Hello World!";

// echo with parentheses (also works)
echo("Hello World!");
?>

🔸 print Statement 


<?php
// print outputs one string
print "Hello World!";

// print returns 1 (can be used in expressions)
$result = print "Hello";  // $result = 1
?>

🔸 Difference Between echo and print

  • echo: Faster, no return value, can take multiple parameters
  • print: Slower, returns 1, takes only one parameter
  • Recommendation: Use echo for most cases (it's more common)

🔹 Common Syntax Errors

Avoid these common mistakes when writing PHP:

❌ Missing Semicolon 

<?php
echo "Hello"  // ERROR: Missing semicolon
echo "World";
?>

✅ Correct Version 

<?php
echo "Hello";  // Semicolon added
echo "World";
?>

❌ Missing PHP Tags 

echo "Hello";  // ERROR: No PHP tags

✅ Correct Version 

<?php
echo "Hello";
?>

❌ Wrong Variable Case 

<?php
$name = "John";
echo $Name;  // ERROR: Undefined variable $Name
?>

✅ Correct Version 

<?php
$name = "John";
echo $name;  // Correct case
?>

🔹 Practice Example

A complete example demonstrating proper PHP syntax: 


<?php
// Proper PHP syntax example

// Variables (case-sensitive)
$firstName = "John";
$lastName = "Doe";
$age = 30;

// Output with echo
echo "<h2>User Profile</h2>";

// Concatenation
echo "<p>Name: " . $firstName . " " . $lastName . "</p>";

// Variable in string
echo "<p>Age: $age years old</p>";

// Calculation
$nextAge = $age + 1;
echo "<p>Next year: $nextAge years old</p>";

// Multiple parameters with echo
echo "<p>", "Status: ", "Active", "</p>";
?>

Output:

User Profile

Name: John Doe

Age: 30 years old

Next year: 31 years old

Status: Active

🧠 Test Your Knowledge

What must every PHP statement end with?