List generic collection in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this C# List operation?

Consider the following C# code that uses a List of integers. What will be printed to the console?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> numbers = new List<int>() {1, 2, 3, 4, 5};
        numbers.RemoveAt(2);
        Console.WriteLine(numbers.Count);
    }
}

A 4

B 5

C 3

D Throws an exception

💡 Hint

Removing an item reduces the count by one.

The list starts with 5 elements. Removing the element at index 2 removes one item, so the count becomes 4.

📝 Syntax

intermediate

Which option correctly adds an element to a List in C#?

You have a List called fruits. Which line of code correctly adds "Apple" to the list?

A fruits.Insert("Apple");

B fruits.Append("Apple");

C fruits.Add("Apple");

D fruits.Push("Apple");

💡 Hint

The method to add an item at the end of a List is Add.

The Add method adds an element to the end of the List. Append is not a List method, Insert requires an index, and Push is not a List method.

❓ optimization

advanced

Which option is the most efficient way to check if a List contains the number 10?

Given a List numbers, which code snippet is the best choice to check if 10 is in the list?

A if (numbers.Find(x => x == 10) != 0) { /* found */ }

B if (numbers.IndexOf(10) != -1) { /* found */ }

C foreach (int n in numbers) { if (n == 10) { /* found */ break; } }

D if (numbers.Contains(10)) { /* found */ }

💡 Hint

Look for the method designed to check existence directly.

Contains is optimized to check if an item exists and returns a boolean. IndexOf returns an index which is less direct. The foreach loop is less concise and slower. Find returns the element or default, which can be confusing if 0 is a valid element.

🔧 Debug

advanced

What error does this code produce?

Examine the following code snippet. What error will it cause when run?

C Sharp (C#)

List<string> names = null;
names.Add("John");

A NullReferenceException

B No error, adds "John"

C InvalidOperationException

D ArgumentNullException

💡 Hint

Think about what happens when you call a method on a null object.

The list 'names' is null, so calling Add on it causes a NullReferenceException.

🧠 Conceptual

expert

What is the time complexity of accessing an element by index in a List?

In C#, what is the time complexity to access an element at a specific index in a List?

A O(n) - Linear time

B O(1) - Constant time

C O(log n) - Logarithmic time

D O(n^2) - Quadratic time

💡 Hint

Think about how List stores elements internally.

List uses an array internally, so accessing by index is constant time O(1).