Null-conditional operator in C Sharp (C#) - Mini Project: Build & Apply

Using the Null-conditional Operator in C#

📖 Scenario: Imagine you are building a simple contact list app. Each contact may or may not have a phone number. You want to safely check if a contact has a phone number without causing errors if the phone number is missing.

🎯 Goal: Learn how to use the null-conditional operator (?.) in C# to safely access properties that might be null.

📋 What You'll Learn

Create a class called Contact with a string property PhoneNumber that can be null.

Create a variable called contact and assign it a new Contact object with no phone number.

Use the null-conditional operator ?. to safely get the length of the phone number string.

Print the length or null if the phone number is missing.

💡 Why This Matters

🌍 Real World

In real apps, data can be missing or optional. The null-conditional operator helps avoid errors when accessing such data.

💼 Career

Understanding null safety is important for writing robust C# code, especially when working with APIs or databases where data might be missing.

1

Create the Contact class and a contact with no phone number

Create a class called Contact with a public string property PhoneNumber that can be null. Then create a variable called contact and assign it a new Contact object with PhoneNumber set to null.

C Sharp (C#)

// Define the Contact class and create a contact with no phone number
// Your code here

Need a hint?

Use string? to allow PhoneNumber to be null.

2

Create a variable to hold the phone number length safely

Create an integer variable called phoneLength and assign it the length of contact.PhoneNumber using the null-conditional operator ?.. Use the null-coalescing operator ?? to assign 0 if the phone number is null.

C Sharp (C#)

public class Contact
{
    public string? PhoneNumber { get; set; }
}

Contact contact = new Contact { PhoneNumber = null };

// Create phoneLength using null-conditional and null-coalescing operators
// Your code here

Need a hint?

Use contact.PhoneNumber?.Length to get length safely, then ?? 0 to default to zero.

3

Change the contact to have a phone number

Change the contact variable so that PhoneNumber is set to the string "123-4567" instead of null.

C Sharp (C#)

public class Contact
{
    public string? PhoneNumber { get; set; }
}

// Change contact to have a phone number
Contact contact = new Contact { PhoneNumber = "123-4567" };

int phoneLength = contact.PhoneNumber?.Length ?? 0;

Need a hint?

Assign the string "123-4567" to PhoneNumber.

4

Print the phone number length

Write a Console.WriteLine statement to print the value of phoneLength.

C Sharp (C#)

public class Contact
{
    public string? PhoneNumber { get; set; }
}

Contact contact = new Contact { PhoneNumber = "123-4567" };

int phoneLength = contact.PhoneNumber?.Length ?? 0;

// Print phoneLength
// Your code here

Need a hint?

Use Console.WriteLine(phoneLength); to show the length.