Null-conditional operator in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the null-conditional operator in C#?

The null-conditional operator is ?. in C#. It allows safe access to members or elements of an object that might be null, preventing exceptions by returning null instead.

beginner

How does ?. help prevent exceptions?

When you use ?., if the object before it is null, the whole expression returns null instead of throwing a NullReferenceException. This makes your code safer and cleaner.

beginner

Example: What does person?.Name do if person is null?

If person is null, person?.Name returns null instead of throwing an error. If person is not null, it returns the Name property.

intermediate

Can the null-conditional operator be used with methods? Give an example.

Yes, you can call a method safely using ?.. For example, person?.GetAge() calls GetAge() only if person is not null. Otherwise, it returns null.

intermediate

What happens when you use the null-conditional operator with an event, like MyEvent?.Invoke()?

Using ?. with events safely invokes the event only if it has subscribers (is not null). This prevents exceptions when no handlers are attached.

What does the null-conditional operator ?. do in C#?

A Safely accesses members of an object that might be null

B Throws an exception if the object is null

C Assigns null to an object

D Checks if an object is not null

The null-conditional operator ?. safely accesses members or methods of an object that might be null, returning null instead of throwing an exception.

What will person?.Name return if person is null?

A Default value of Name's type

B Empty string

C Throws NullReferenceException

D null

If person is null, person?.Name returns null safely without throwing an exception.

Which of these is a valid use of the null-conditional operator?

A person?.GetAge()

B person.GetAge()?

C person?GetAge()

D person.GetAge?.()

person?.GetAge() safely calls the method only if person is not null.

How does MyEvent?.Invoke() help when raising events?

A It always invokes the event

B It unsubscribes all handlers

C It invokes the event only if there are subscribers

D It throws an exception if no subscribers

Using ?. with events invokes the event only if it has subscribers, preventing exceptions.

What type of value does the null-conditional operator return when the object is null?

A Default value of the member

B null

C Empty string

D Zero

When the object is null, the null-conditional operator returns null instead of throwing an error.

Explain how the null-conditional operator ?. works and why it is useful in C#.

Think about how it helps avoid errors when objects might be missing.

Describe a scenario where using ?. with an event is beneficial.

Consider what happens if you try to raise an event with no listeners.