Null type and its meaning in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign a null value to the variable.

PHP

<?php
$var = [1];
?>

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

Afalse

B0

C"null"

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or false instead of null.

Using the string "null" instead of the null value.

In PHP, null is the special value used to represent a variable with no value.

2fill in blank

medium

Complete the code to check if a variable is null.

PHP

<?php
if ([1]($var)) {
    echo "Variable is null.";
}
?>

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

Ais_null

Bisset

Cempty

Dis_string

Attempts:

3 left

💡 Hint

Common Mistakes

Using isset() which returns false if variable is null but also false if variable is not set.

Using empty() which returns true for many values, not just null.

The function is_null() returns true if the variable is null.

3fill in blank

hard

Fix the error in the code to correctly assign null to the variable.

PHP

<?php
$var = [1];
?>

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

ANULL

BNull

Cnull

D"null"

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase NULL, which is accepted but lowercase is preferred.

Using quotes which makes it a string, not null.

In PHP, the null value is null (case-insensitive, but lowercase is standard and preferred). Using quotes makes it a string, not null.

4fill in blank

hard

Fill both blanks to create an array with keys and values where some values are null.

PHP

<?php
$data = [
    'name' => 'Alice',
    'age' => [1],
    'email' => [2]
];
?>

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

Anull

B"[e-mail]"

C0

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or false instead of null for missing age.

Not using quotes around the email string.

The 'age' key has a null value, meaning no age is set. The 'email' key has a string value.

5fill in blank

hard

Fill all three blanks to create a function that returns null if input is empty, else returns input.

PHP

<?php
function checkInput($input) {
    if (empty($input)) {
        return [1];
    } else {
        return [2];
    }
}

$result = checkInput([3]);
?>

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

Anull

B$input

C""

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 0 or false instead of null for empty input.

Not returning the input variable in the else branch.

Calling the function with a value other than an empty string.

The function returns null if the input is empty (like an empty string), otherwise it returns the input itself. The function is called with an empty string.

Practice

1. What does the null type represent in PHP?

easy

A. A variable with no value assigned

B. A variable holding the number zero

C. A variable holding an empty string

D. A variable holding a boolean false

Solution

1. Step 1: Understand the meaning of null in PHP

   Null means the variable does not have any value assigned to it.

2. Step 2: Differentiate null from other values

   Zero, empty string, and false are actual values, but null means no value.

3. Final Answer:

   A variable with no value assigned -> Option A

4. Quick Check:

   Null means no value = D [OK]

Hint: Null means no value, not zero or empty [OK]

Common Mistakes:

• Confusing null with zero
• Thinking null is an empty string
• Assuming null is false

2. Which of the following is the correct way to assign a null value to a variable in PHP?

easy

A. $var = 'null';

B. $var == null;

C. $var := null;

D. $var = null;

Solution

1. Step 1: Identify correct assignment syntax in PHP

   Assignment uses a single equals sign = in PHP.

2. Step 2: Check how to assign null

   Null is assigned as null without quotes, so $var = null; is correct.

3. Final Answer:

   $var = null; -> Option D

4. Quick Check:

   Assign null with = null; = C [OK]

Hint: Use single = and null without quotes [OK]

Common Mistakes:

• Using 'null' as a string
• Using == instead of = for assignment
• Using := which is invalid in PHP

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

$var = null;
if ($var === null) {
    echo 'Yes';
} else {
    echo 'No';
}

medium

A. Yes

B. No

C. null

D. Error

Solution

1. Step 1: Understand strict comparison with ===

   The operator === checks both value and type. Since $var is null, $var === null is true.

2. Step 2: Determine which branch runs

   Because condition is true, the code echoes 'Yes'.

3. Final Answer:

   Yes -> Option A

4. Quick Check:

   $var === null is true, so output is Yes [OK]

Hint: Use === to check exact null value [OK]

Common Mistakes:

• Using == which can be true for other falsy values
• Expecting output 'null' instead of 'Yes'
• Confusing echo output with variable value

4. Identify the error in this PHP code snippet:

$var = null
if ($var === null) {
    echo 'Null value';
}

medium

A. Incorrect comparison operator

B. Missing semicolon after assignment

C. Null cannot be assigned to variables

D. Echo statement syntax error

Solution

1. Step 1: Check syntax of assignment line

   The line $var = null is missing a semicolon at the end, which is required in PHP.

2. Step 2: Verify other parts of the code

   The comparison and echo statements are correct and valid.

3. Final Answer:

   Missing semicolon after assignment -> Option B

4. Quick Check:

   Every statement needs ; in PHP [OK]

Hint: Check for missing semicolons after statements [OK]

Common Mistakes:

• Forgetting semicolon after assignment
• Thinking null can't be assigned
• Misreading === as wrong operator

5. You want to check if a variable $data has no value assigned and then assign it a default string 'empty'. Which code correctly does this in PHP?

hard

A. if (is_null($data)) { $data = 'empty'; }

B. if ($data === null) { $data = 'empty'; }

C. All of the above

D. if ($data == null) { $data = 'empty'; }

Solution

1. Step 1: Understand ways to check for null

   In PHP, $data == null, $data === null, and is_null($data) all check if variable is null, with slight differences.

2. Step 2: Confirm assignment after check

   All three conditions correctly assign 'empty' if $data is null.

3. Step 3: Evaluate correctness of all options

   Since options B, C, and D work, the correct choice is 'All of the above'.

4. Final Answer:

   All of the above -> Option C

5. Quick Check:

   Multiple ways to check null = A [OK]

Hint: Use any null check method before assigning default [OK]

Common Mistakes:

• Thinking only === works for null check
• Ignoring is_null() function
• Confusing == with === always