Class declaration syntax in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple PHP class method call

What is the output of this PHP code?

PHP

<?php
class Greeting {
    public function sayHello() {
        return "Hello, world!";
    }
}
$greet = new Greeting();
echo $greet->sayHello();
?>

A Parse error: syntax error, unexpected 'return'

B Hello, world!

C Fatal error: Call to undefined method Greeting::sayHello()

D Hello world

💡 Hint

Look at the method name and how it is called on the object.

The class Greeting has a public method sayHello() that returns the string "Hello, world!". The object $greet calls this method correctly, so the output is exactly that string.

❓ Predict Output

intermediate

Output when accessing a private property directly

What happens when this PHP code runs?

PHP

<?php
class Person {
    private string $name = "Alice";
}
$p = new Person();
echo $p->name;
?>

A Alice

B Notice: Undefined property: Person::$name

C Fatal error: Uncaught Error: Cannot access private property Person::$name

D Parse error: syntax error, unexpected 'string'

💡 Hint

Check the visibility of the property and how it is accessed.

The property $name is declared private, so it cannot be accessed directly outside the class. Trying to echo $p->name causes a fatal error about accessing a private property.

🔧 Debug

advanced

Identify the syntax error in this class declaration

This PHP code has a syntax error. Which option shows the exact error message produced when running it?

PHP

<?php
class Car {
    public $make;
    public $model
    public function __construct($make, $model) {
        $this->make = $make;
        $this->model = $model;
    }
}
?>

A Parse error: syntax error, unexpected 'public' (T_PUBLIC) in line 4

B Fatal error: Cannot redeclare class Car

C Notice: Undefined variable: model

D Parse error: syntax error, unexpected '$make' (T_VARIABLE) in line 5

💡 Hint

Look carefully at the property declarations and missing punctuation.

The property $model is missing a semicolon at the end of its declaration line, so the parser finds 'public' keyword unexpectedly on the next line, causing a syntax error.

❓ Predict Output

advanced

Output of static property access in PHP class

What is the output of this PHP code?

PHP

<?php
class Counter {
    public static int $count = 0;
    public function __construct() {
        self::$count++;
    }
}
new Counter();
new Counter();
echo Counter::$count;
?>

A 1

B 0

C Fatal error: Access to undeclared static property Counter::$count

D 2

💡 Hint

Static properties are shared across all instances of the class.

Each time a new Counter object is created, the static property $count is incremented by 1. After creating two objects, $count is 2.

❓ Predict Output

expert

Output of class constant and method call

What is the output of this PHP code?

PHP

<?php
class MathConstants {
    public const PI = 3.14;
    public static function getPi() {
        return self::PI;
    }
}
echo MathConstants::PI . ' ' . MathConstants::getPi();
?>

A 3.14 3.14

B PI 3.14

C 3.14 getPi

D Fatal error: Access to undefined constant PI

💡 Hint

Class constants are accessed with :: and can be used inside static methods with self::

The constant PI is defined as 3.14. Accessing MathConstants::PI returns 3.14. The static method getPi() returns self::PI, also 3.14. So the output is '3.14 3.14'.

Practice

1. What is the correct way to start declaring a class named Car in PHP?

easy

A. class Car { }

B. function Car() { }

C. Car class { }

D. declare class Car { }

Solution

1. Step 1: Understand PHP class declaration syntax

   In PHP, classes are declared using the keyword class followed by the class name and curly braces.

2. Step 2: Match the syntax to the options

   class Car { } uses class Car { }, which is the correct syntax. Other options use incorrect keywords or order.

3. Final Answer:

   class Car { } -> Option A

4. Quick Check:

   PHP class declaration = class ClassName { } [OK]

Hint: Look for 'class' keyword followed by name and braces [OK]

Common Mistakes:

• Using 'function' instead of 'class'
• Placing 'class' after the name
• Adding extra keywords like 'declare'

2. Which of the following is the correct syntax to declare an empty class named Person in PHP?

easy

A. class Person() { }

B. class Person[] { }

C. class Person {};

D. class Person { }

Solution

1. Step 1: Recall PHP class declaration syntax

   PHP classes are declared with the keyword class, the class name, and curly braces without parentheses or brackets.

2. Step 2: Check each option

   class Person { } uses class Person { }, which is correct. class Person() { } wrongly uses parentheses, B uses brackets, and D adds a semicolon after braces which is unnecessary.

3. Final Answer:

   class Person { } -> Option D

4. Quick Check:

   Empty class = class Name { } [OK]

Hint: No parentheses or brackets after class name [OK]

Common Mistakes:

• Adding parentheses after class name
• Using square brackets after class name
• Adding unnecessary semicolon after class braces

3. What will be the output of this PHP code?

class Dog {
  public $name = "Buddy";
}
$dog = new Dog();
echo $dog->name;

medium

A. Buddy

B. Dog

C. Error: Undefined property

D. null

Solution

1. Step 1: Understand the class and property

   The class Dog has a public property $name set to "Buddy".

2. Step 2: Create an object and access property

   Creating $dog = new Dog(); makes an object. Accessing $dog->name returns "Buddy".

3. Final Answer:

   Buddy -> Option A

4. Quick Check:

   Access public property = property value [OK]

Hint: Public properties can be accessed directly via object [OK]

Common Mistakes:

• Expecting class name instead of property value
• Forgetting to create an object before access
• Assuming property is private and inaccessible

4. Identify the error in this PHP class declaration:

class Animal
  public $type;
}

medium

A. Class name should be lowercase

B. Missing opening brace { after class name

C. Property must be static

D. Missing semicolon after class name

Solution

1. Step 1: Check class declaration syntax

   PHP classes require an opening brace { immediately after the class name.

2. Step 2: Analyze the given code

   The code has no opening brace after class Animal, causing a syntax error.

3. Final Answer:

   Missing opening brace { after class name -> Option B

4. Quick Check:

   Class declaration needs { after name [OK]

Hint: Always put { right after class name [OK]

Common Mistakes:

• Omitting opening brace {
• Thinking semicolon needed after class name
• Confusing property declaration rules

5. You want to declare a PHP class Book with a property $title initialized to "PHP Basics" and a method getTitle() that returns the title. Which is the correct class declaration?

hard

A. class Book {
public $title;
public function getTitle() {
return $title;
}
}

B. class Book {
public $title = "PHP Basics";
function getTitle() {
return title;
}
}

C. class Book {
public $title = "PHP Basics";
public function getTitle() {
return $this->title;
}
}

D. class Book {
public $title = "PHP Basics";
public function getTitle() {
return $Book->title;
}
}

Solution

1. Step 1: Declare property with initial value

   Property $title is declared public and initialized to "PHP Basics" correctly in class Book { public $title = "PHP Basics"; public function getTitle() { return $this->title; } }.

2. Step 2: Define method returning property

   Method getTitle() must return $this->title to access the object's property. class Book { public $title = "PHP Basics"; public function getTitle() { return $this->title; } } does this correctly.

3. Step 3: Check other options for errors

   class Book { public $title = "PHP Basics"; function getTitle() { return title; } } returns title without $this->, class Book { public $title; public function getTitle() { return $title; } } returns $title which is undefined in method scope, class Book { public $title = "PHP Basics"; public function getTitle() { return $Book->title; } } uses $Book->title which is invalid inside class.

4. Final Answer:

   class Book { public $title = "PHP Basics"; public function getTitle() { return $this->title; } } -> Option C

5. Quick Check:

   Use $this->property inside methods [OK]

Hint: Use $this->property to access inside methods [OK]

Common Mistakes:

• Returning property without $this-> inside method
• Using variable names without $this->
• Trying to access property with class name variable