Nullable value types in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Nullable Int Addition

What is the output of this C# code snippet?

C Sharp (C#)

int? a = 5;
int? b = null;
var result = a + b;
Console.WriteLine(result == null ? "null" : result.ToString());

A 0

B null

C 5

D Compilation error

💡 Hint

Adding a nullable int with null results in null.

When you add a nullable int with a null value, the result is null because the operation propagates null.

🧠 Conceptual

intermediate

Nullable Boolean Default Value

What is the default value of a nullable bool declared as bool? flag; before any assignment?

A null

B false

C true

D Compilation error

💡 Hint

Nullable types default to null if not assigned.

Nullable value types default to null when declared but not assigned any value.

🔧 Debug

advanced

Fix the NullReferenceException

This code throws a NullReferenceException. Which option fixes it?

C Sharp (C#)

int? x = null;
int y = x.Value;
Console.WriteLine(y);

A int y = x.GetValueOrDefault();

B int y = (int)x;

C int y = x ?? 0;

D int y = x.Value ?? 0;

💡 Hint

Use the null-coalescing operator to provide a default value.

Accessing Value on a null nullable throws an exception. Using 'x ?? 0' safely provides 0 if x is null.

📝 Syntax

advanced

Identify the Syntax Error

Which option contains a syntax error when declaring a nullable int?

A int? number = 10;

B Nullable<int> number = null;

C int? number = null;

D int? number = ?5;

💡 Hint

Check the placement of the question mark.

The question mark must come after the type, not before the value.

🚀 Application

expert

Count Non-Null Nullable Integers

Given this list of nullable integers, what is the count of non-null values?

List numbers = new() { 1, null, 3, null, 5 };

C Sharp (C#)

List<int?> numbers = new() { 1, null, 3, null, 5 };
int count = numbers.Count(n => n.HasValue);
Console.WriteLine(count);

A 3

B 2

C 5

D Compilation error

💡 Hint

Use the HasValue property to check for non-null values.

The list has three non-null values: 1, 3, and 5. Counting those gives 3.