Constants in classes in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constant named PI with value 3.14 inside the class.

PHP

<?php
class Circle {
    const [1] = 3.14;
}
?>

Drag options to blanks, or click blank then click option'

Api

BPI

CRadius

DVALUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase constant names like 'pi' instead of 'PI'.

Trying to use variables instead of constants.

The constant name is PI as per convention and the problem statement.

2fill in blank

medium

Complete the code to access the constant PI from the Circle class.

PHP

<?php
class Circle {
    const PI = 3.14;
}
echo Circle::[1];
?>

Drag options to blanks, or click blank then click option'

API

Bpi

CRadius

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'pi' instead of 'PI'.

Trying to access constants like variables with $.

Constants are accessed using the class name, double colon, and the constant name exactly as declared, which is PI.

3fill in blank

hard

Fix the error in the code to correctly access the constant MAX_SPEED inside the Car class.

PHP

<?php
class Car {
    const MAX_SPEED = 200;
    public function getMaxSpeed() {
        return self::[1];
    }
}
?>

Drag options to blanks, or click blank then click option'

A$MAX_SPEED

Bmax_speed

CMax_Speed

DMAX_SPEED

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or camel case names instead of uppercase.

Using $ sign before constant name.

Inside the class, constants are accessed with self::CONSTANT_NAME using the exact constant name MAX_SPEED.

4fill in blank

hard

Fill both blanks to define a constant SPEED_LIMIT and access it inside the class method.

PHP

<?php
class Bike {
    const [1] = 100;
    public function getSpeedLimit() {
        return self::[2];
    }
}
?>

Drag options to blanks, or click blank then click option'

ASPEED_LIMIT

Bspeed_limit

CMAX_SPEED

DLIMIT

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for declaration and access.

Using lowercase names for constants.

The constant name must be the same in both declaration and access: SPEED_LIMIT.

5fill in blank

hard

Fill all three blanks to define a constant COLOR, access it inside the class, and print it outside the class.

PHP

<?php
class Car {
    const [1] = 'red';
    public function getColor() {
        return self::[2];
    }
}
echo Car::[3];
?>

Drag options to blanks, or click blank then click option'

Acolor

BCOLOR

CColor

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or different case names.

Trying to access constants like variables.

The constant name is COLOR and must be used exactly as declared both inside and outside the class.

Practice

1. What keyword is used to declare a constant inside a PHP class?

easy

A. let

B. var

C. const

D. static

Solution

1. Step 1: Understand constant declaration in PHP classes

   In PHP, constants inside classes are declared using the const keyword, which defines a fixed value that cannot change.

2. Step 2: Differentiate from other keywords

   var is used for properties (deprecated), let is not a PHP keyword, and static is for static properties or methods, not constants.

3. Final Answer:

   const -> Option C

4. Quick Check:

   Class constants use const keyword [OK]

Hint: Use 'const' to declare fixed values in classes [OK]

Common Mistakes:

• Using 'var' instead of 'const'
• Trying to use 'let' which is not PHP
• Confusing 'static' with constants

2. Which of the following is the correct syntax to access a class constant named VERSION in PHP?

easy

A. ClassName::VERSION

B. $obj->VERSION

C. ClassName->VERSION

D. $obj:VERSION

Solution

1. Step 1: Recall how to access class constants

   Class constants are accessed using the scope resolution operator :: with the class name, like ClassName::CONSTANT.

2. Step 2: Identify incorrect options

   $obj->VERSION tries to access a property, not a constant; ClassName->VERSION is invalid syntax; $obj:VERSION uses single colon which is invalid syntax.

3. Final Answer:

   ClassName::VERSION -> Option A

4. Quick Check:

   Access constants with ClassName::CONSTANT [OK]

Hint: Use ClassName::CONSTANT to access class constants [OK]

Common Mistakes:

• Using object operator -> instead of ::
• Trying to access constants as properties
• Confusing variable and class name usage

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

class Car {
    const WHEELS = 4;
}
echo Car::WHEELS;

medium

A. 4

B. WHEELS

C. Error: Undefined constant

D. null

Solution

1. Step 1: Identify the constant declaration

   The class Car declares a constant WHEELS with value 4.

2. Step 2: Understand the echo statement

   The code prints the value of Car::WHEELS, which is 4.

3. Final Answer:

   4 -> Option A

4. Quick Check:

   Class constant value printed = 4 [OK]

Hint: ClassName::CONSTANT prints the constant's value [OK]

Common Mistakes:

• Expecting the name 'WHEELS' to print
• Thinking it causes an error
• Confusing constants with variables

4. What is wrong with this PHP code?

class Book {
    const TITLE = 'PHP Basics';
}

$book = new Book();
echo $book::TITLE;

medium

A. Cannot access constant via object instance with ::

B. Constant TITLE is not declared correctly

C. Missing semicolon after constant declaration

D. Code will output 'PHP Basics' without error

Solution

1. Step 1: Verify constant declaration

   The class Book correctly declares const TITLE = 'PHP Basics';.

2. Step 2: Verify access syntax

   $book = new Book(); creates an instance, and $book::TITLE is valid syntax to access the class constant from an instance. The code outputs PHP Basics without error.

3. Final Answer:

   Code will output 'PHP Basics' without error -> Option D

4. Quick Check:

   $instance::CONSTANT is valid [OK]

Hint: ClassName::CONSTANT or $instance::CONSTANT both valid [OK]

Common Mistakes:

• Using -> for constants instead of ::
• Declaring with var instead of const
• Thinking $instance::CONSTANT is invalid

5. Given the class below, which code correctly prints the constant STATUS without creating an object?

class Server {
    const STATUS = 'Online';
}

hard

A. echo Server->STATUS;

B. echo Server::STATUS;

C. echo $server::STATUS;

D. echo Server::status;

Solution

1. Step 1: Identify correct constant access syntax

   Constants are accessed using the class name and the scope resolution operator :: with the exact constant name in uppercase.

2. Step 2: Evaluate each option

   Server->STATUS is invalid because -> is for object properties; $server::STATUS is invalid because $server is undefined and constants should be accessed via class name; Server::status is wrong due to case sensitivity; only Server::STATUS is correct.

3. Final Answer:

   echo Server::STATUS; -> Option B

4. Quick Check:

   Use ClassName::CONSTANT with exact case [OK]

Hint: Use ClassName::CONSTANT with exact uppercase name [OK]

Common Mistakes:

• Using object operator -> instead of ::
• Ignoring case sensitivity in constant names
• Trying to access constants via undefined variables