First, Single, and their OrDefault variants in C Sharp (C#) - Mini Project: Build & Apply

Using First, Single, and Their OrDefault Variants in C#

📖 Scenario: You are working on a simple program that manages a list of book titles in a library. You want to find specific books using different methods that help you get the first match, a single match, or a safe default if no match is found.

🎯 Goal: Build a C# program that uses First, Single, FirstOrDefault, and SingleOrDefault methods to find books in a list safely and correctly.

📋 What You'll Learn

Create a list of book titles with exact values.

Add a search keyword variable.

Use First and Single methods to find books.

Use FirstOrDefault and SingleOrDefault methods to handle cases with no matches.

Print the results clearly.

💡 Why This Matters

🌍 Real World

Finding specific items in lists or collections is common in apps like libraries, stores, or contact lists.

💼 Career

Understanding these LINQ methods helps you write safer and clearer code when searching data in professional C# development.

1

Create a list of book titles

Create a List<string> called books with these exact titles: "C# Basics", "LINQ Fundamentals", "C# Basics", "Advanced C#".

C Sharp (C#)

// Create the list of books below
// Your code here

Need a hint?

Use new List<string> { ... } to create the list with the exact titles.

2

Add a search keyword variable

Add a string variable called searchKeyword and set it to "C# Basics".

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List books = new List { "C# Basics", "LINQ Fundamentals", "C# Basics", "Advanced C#" };
        // Add the searchKeyword variable below
        // Your code here
    }
}

Need a hint?

Declare a string variable with the exact name and value.

3

Use First and Single to find books

Use First to find the first book in books that equals searchKeyword and store it in firstBook. Then use Single to find the single book in books that equals "LINQ Fundamentals" and store it in singleBook.

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List books = new List { "C# Basics", "LINQ Fundamentals", "C# Basics", "Advanced C#" };
        string searchKeyword = "C# Basics";
        // Use First to find firstBook
        // Use Single to find singleBook
        // Your code here
    }
}

Need a hint?

Use books.First(book => book == searchKeyword) and books.Single(book => book == "LINQ Fundamentals").

4

Use OrDefault variants and print results

Use FirstOrDefault to find a book matching "Nonexistent Book" and store it in firstOrDefaultBook. Use SingleOrDefault to find a book matching "Advanced C#" and store it in singleOrDefaultBook. Then print all four variables: firstBook, singleBook, firstOrDefaultBook, and singleOrDefaultBook.

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List books = new List { "C# Basics", "LINQ Fundamentals", "C# Basics", "Advanced C#" };
        string searchKeyword = "C# Basics";
        string firstBook = books.First(book => book == searchKeyword);
        string singleBook = books.Single(book => book == "LINQ Fundamentals");
        // Use FirstOrDefault and SingleOrDefault
        // Print all results
        // Your code here
    }
}

Need a hint?

Use FirstOrDefault and SingleOrDefault with the exact search strings. Use Console.WriteLine to print each result. Use ?? "null" to show "null" if the result is empty.