List methods (Add, Remove, Find, Sort) in C Sharp (C#) - Mini Project: Build & Apply

List methods (Add, Remove, Find, Sort)

📖 Scenario: You are managing a small library's book collection. You want to keep track of book titles, add new books, remove old ones, find specific books, and keep the list sorted alphabetically.

🎯 Goal: Build a simple C# program that uses a list of book titles and applies common list methods: Add, Remove, Find, and Sort.

📋 What You'll Learn

Create a list of strings called books with exact initial titles

Add a new book title to the books list

Remove a specific book title from the books list

Find a book title in the books list using Find

Sort the books list alphabetically

Print the final sorted list of books

💡 Why This Matters

🌍 Real World

Managing collections of items like books, products, or contacts often requires adding, removing, searching, and sorting data.

💼 Career

These list methods are fundamental in many programming jobs, especially when working with collections of data in applications.

1

Create the initial list of books

Create a list of strings called books with these exact titles: "The Hobbit", "1984", "Brave New World", "Fahrenheit 451".

C Sharp (C#)

# Create the list of books with the exact titles
# Your code here

Hint

Use List<string> and initialize it with the four book titles inside curly braces.

2

Add a new book to the list

Add the book title "Animal Farm" to the books list using the Add method.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List books = new List { "The Hobbit", "1984", "Brave New World", "Fahrenheit 451" };
        // Add "Animal Farm" to the books list
        // Your code here
    }
}

Hint

Use books.Add("Animal Farm") to add the new book.

3

Remove a book from the list

Remove the book titled "1984" from the books list using the Remove method.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List books = new List { "The Hobbit", "1984", "Brave New World", "Fahrenheit 451" };
        books.Add("Animal Farm");
        // Remove "1984" from the books list
        // Your code here
    }
}

Hint

Use books.Remove("1984") to remove the book.

4

Find and sort the books, then print the list

Use the Find method on books to find the book titled "Animal Farm" and store it in a variable called foundBook. Then sort the books list alphabetically using Sort. Finally, print each book title on its own line using a foreach loop.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List books = new List { "The Hobbit", "1984", "Brave New World", "Fahrenheit 451" };
        books.Add("Animal Farm");
        books.Remove("1984");
        // Find "Animal Farm" and store in foundBook
        // Sort the books list
        // Print each book title
        // Your code here
    }
}

Hint

Use string foundBook = books.Find(book => book == "Animal Farm") to find the book. Then call books.Sort(). Use a foreach loop to print each book.

Practice

1. Which List method in C# is used to add a new item to the end of the list?

easy

A. Sort

B. Remove

C. Find

D. Add

Solution

1. Step 1: Understand the purpose of Add

   The Add method appends a new element to the end of a list.

2. Step 2: Compare with other methods

   Remove deletes items, Find searches, and Sort arranges items, so they don't add new items.

3. Final Answer:

   Add -> Option D

4. Quick Check:

   Add method adds items [OK]

Hint: Add puts new items at the list's end [OK]

Common Mistakes:

• Confusing Remove with Add
• Thinking Find adds items
• Assuming Sort adds items

2. Which of the following is the correct syntax to remove the first occurrence of "apple" from a List<string> named fruits?

easy

A. fruits.RemoveAt("apple");

B. fruits.Delete("apple");

C. fruits.Remove("apple");

D. fruits.RemoveItem("apple");

Solution

1. Step 1: Identify the correct method name

   The method to remove an item by value is Remove, so fruits.Remove("apple") is correct.

2. Step 2: Check method parameters and usage

   RemoveAt requires an index, not a string. Delete and RemoveItem are not valid List methods.

3. Final Answer:

   fruits.Remove("apple"); -> Option C

4. Quick Check:

   Remove("apple") removes first matching item [OK]

Hint: Use Remove with the item value to delete it [OK]

Common Mistakes:

• Using RemoveAt with a string argument
• Using non-existent methods like Delete or RemoveItem
• Confusing Remove with Add

3. What will be the output of the following C# code?

var numbers = new List<int> {5, 3, 8, 1};
numbers.Sort();
Console.WriteLine(string.Join(",", numbers));

medium

A. 5,3,8,1

B. 1,3,5,8

C. 8,5,3,1

D. 3,5,1,8

Solution

1. Step 1: Understand what Sort does

   Sort arranges the list items in ascending order.

2. Step 2: Apply Sort to the list

   The list {5, 3, 8, 1} sorted ascending becomes {1, 3, 5, 8}.

3. Final Answer:

   1,3,5,8 -> Option B

4. Quick Check:

   Sort orders numbers ascending [OK]

Hint: Sort arranges numbers from smallest to largest [OK]

Common Mistakes:

• Assuming Sort reverses the list
• Confusing Sort with Find
• Expecting original order after Sort

4. Identify the error in this code snippet:

var fruits = new List<string> {"apple", "banana", "cherry"};
fruits.RemoveAt("banana");

medium

A. RemoveAt expects an index, not a string

B. RemoveAt cannot be used on List<string>

C. RemoveAt removes all matching items

D. RemoveAt adds an item instead of removing

Solution

1. Step 1: Check RemoveAt parameter type

   RemoveAt requires an integer index, but "banana" is a string.

2. Step 2: Understand method behavior

   Using a string causes a compile-time error because the argument type is wrong.

3. Final Answer:

   RemoveAt expects an index, not a string -> Option A

4. Quick Check:

   RemoveAt needs index integer [OK]

Hint: RemoveAt uses index number, not item value [OK]

Common Mistakes:

• Passing item value instead of index to RemoveAt
• Thinking RemoveAt removes all matches
• Confusing RemoveAt with Remove

5. Given a List<int> numbers = new List<int> {4, 7, 2, 9, 3}; which code snippet correctly finds the first number greater than 5 and removes it from the list?

hard

A. var num = numbers.Find(n => n > 5);
numbers.Remove(num);

B. numbers.RemoveAt(numbers.Find(n => n > 5));

C. numbers.Remove(numbers.FindIndex(n => n > 5));

D. numbers.Remove(numbers.Find(n => n < 5));

Solution

1. Step 1: Use Find to get first number > 5

   Find returns the first element matching the condition n > 5, which is 7.

2. Step 2: Remove that number from the list

   Remove(num) deletes the first occurrence of 7 from the list.

3. Final Answer:

   var num = numbers.Find(n => n > 5); numbers.Remove(num); -> Option A

4. Quick Check:

   Find returns item, Remove deletes it [OK]

Hint: Find returns item; Remove deletes that item [OK]

Common Mistakes:

• Passing Find result directly to RemoveAt (wrong type)
• Using FindIndex result with Remove (expects item, not index)
• Searching for wrong condition (n < 5 instead of n > 5)