Null type and its meaning in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the null type represent in PHP?

The null type represents a variable with no value or an empty value. It means the variable is explicitly set to have no data.

beginner

How do you assign a null value to a variable in PHP?

You assign null by writing: $var = null;. This means $var holds no value.

intermediate

What is the difference between an uninitialized variable and a variable set to null in PHP?

An uninitialized variable has never been given a value, while a variable set to null has been explicitly assigned no value.

beginner

What does the function is_null() do in PHP?

The is_null() function checks if a variable is null. It returns true if the variable is null, otherwise false.

beginner

Can a variable of any type be set to null in PHP?

Yes, in PHP any variable can be set to null, which means it no longer holds its previous value.

What does null mean in PHP?

A Variable holds false

B Variable holds zero

C Variable holds an empty string

D Variable has no value

null means the variable has no value at all, not zero, empty string, or false.

How do you check if a variable is null in PHP?

A Using <code>isset()</code>

B Using <code>empty()</code>

C Using <code>is_null()</code>

D Using <code>is_string()</code>

is_null() returns true if the variable is null.

What happens if you assign null to a variable that had a value before?

A It keeps the old value

B It loses its previous value

C It becomes zero

D It becomes an empty array

Assigning null removes the previous value from the variable.

Which of these is NOT true about null in PHP?

A <code>null</code> is the same as false

B <code>null</code> means no value

C Variables can be set to <code>null</code>

D <code>is_null()</code> checks for <code>null</code>

null is different from false; false is a boolean, null means no value.

What is the result of isset($var) if $var = null;?

A false

B true

C null

D error

isset() returns false if the variable is null.

Explain what the null type means in PHP and how it is used.

Think about how you tell PHP a variable has no data.

Describe how to check if a variable is null and what happens when you assign null to a variable.

Consider the functions and effects on the variable.