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

Recall & Review

beginner

What does the null-coalescing operator (??) do in C#?

It returns the left-hand operand if it is not null; otherwise, it returns the right-hand operand.

beginner

How would you use the null-coalescing operator to provide a default value for a nullable variable?

Example: int? x = null; int y = x ?? 10; Here, y will be 10 because x is null.

intermediate

Can the null-coalescing operator be chained? If yes, how?

Yes, you can chain it like a ?? b ?? c. It returns the first non-null value from left to right.

intermediate

What is the difference between the null-coalescing operator (??) and the ternary operator when checking for null?

The null-coalescing operator is a concise way to check for null and provide a default, while the ternary operator requires a full condition like x != null ? x : defaultValue.

beginner

Write a simple C# code snippet using the null-coalescing operator to assign a string variable a default value if it is null.

string name = null;
string displayName = name ?? "Guest";
// displayName will be "Guest" if name is null

What will the expression int? a = null; int b = a ?? 5; assign to b?

A 5

B null

C 0

D Compilation error

Since 'a' is null, the null-coalescing operator returns the right side value 5.

Which operator is used in C# to return the first non-null value between two expressions?

A ??

B ?:

C &&

D ||

The null-coalescing operator '??' returns the left operand if not null; otherwise, the right operand.

What will string s = null; var result = s ?? "default"; set result to?

A Compilation error

B "default"

C Empty string

D null

Since s is null, the operator returns the right side string "default".

Can the null-coalescing operator be used with non-nullable value types directly?

A Yes, with any type

B Only with integers

C Only with strings

D No, only with nullable types or reference types

It works with nullable types or reference types because they can be null.

What is the output of string? name = "Alice"; var display = name ?? "Guest";?

A null

B "Guest"

C "Alice"

D Compilation error

Since name is not null, the operator returns "Alice".

Explain how the null-coalescing operator (??) works in C# and give a simple example.

Think about providing a default value when something might be null.

Describe a scenario where chaining the null-coalescing operator is useful and how it works.

Imagine checking several options until you find one that is not null.