Node Structure and Pointer Design in DSA C# - Build from Scratch

Node Structure and Pointer Design

📖 Scenario: Imagine you are building a simple linked list to keep track of tasks in a to-do list app. Each task is a node that stores the task name and a pointer to the next task.

🎯 Goal: You will create a basic Node class with a string value and a pointer to the next node. Then, you will link two nodes together and print the list.

📋 What You'll Learn

Create a Node class with a public string field TaskName and a public Node field Next.

Create two Node objects with task names exactly "Buy groceries" and "Clean room".

Link the first node's Next pointer to the second node.

Print the task names in order by following the Next pointers.

💡 Why This Matters

🌍 Real World

Linked lists are used in many apps to manage lists where items can be added or removed easily, like task lists, music playlists, or undo history.

💼 Career

Understanding node structures and pointers is essential for software developers working with data structures, memory management, and building efficient algorithms.

1

Create the Node class

Create a public class called Node with a public string field TaskName and a public Node field Next.

DSA C#

# Your code here

Hint

Think of Node as a box that holds a task name and a pointer to the next box.

2

Create two Node objects

Create two Node objects called firstTask and secondTask. Set firstTask.TaskName to "Buy groceries" and secondTask.TaskName to "Clean room".

DSA C#

public class Node
{
    public string TaskName;
    public Node Next;
}

// Your code here

Hint

Create each node and assign the task name exactly as shown.

3

Link the nodes

Set the Next pointer of firstTask to point to secondTask.

DSA C#

public class Node
{
    public string TaskName;
    public Node Next;
}

Node firstTask = new Node();
firstTask.TaskName = "Buy groceries";
Node secondTask = new Node();
secondTask.TaskName = "Clean room";

// Your code here

Hint

Link the first task's Next field to the second task.

4

Print the linked list

Use a Node variable called current to start at firstTask. Use a while loop to print current.TaskName and then move current to current.Next. Stop when current is null.

DSA C#

public class Node
{
    public string TaskName;
    public Node Next;
}

Node firstTask = new Node();
firstTask.TaskName = "Buy groceries";
Node secondTask = new Node();
secondTask.TaskName = "Clean room";

firstTask.Next = secondTask;

// Your code here

Hint

Use a loop to follow the Next pointers and print each task name.

Practice

1. What is the primary purpose of the next pointer in a singly linked list node?

easy

A. To store the data value of the node

B. To point to the previous node in the list

C. To point to the next node in the list

D. To indicate the end of the list

Solution

1. Step 1: Understand the role of pointers in linked lists

   In a singly linked list, each node contains data and a pointer to the next node to maintain the sequence.

2. Step 2: Identify the function of the next pointer

   The next pointer specifically points to the next node, allowing traversal through the list.

3. Final Answer:

   To point to the next node in the list -> Option C

4. Quick Check:

   next pointer = points to next node [OK]

Hint: Remember: next always moves forward in the list [OK]

Common Mistakes:

• Confusing next with previous pointer
• Thinking next stores data
• Assuming next marks list end

2. Which of the following is the correct way to declare a node class with a pointer to the next node in C#?

easy

A. public class Node { int data; Node next; void Node() {} }

B. public class Node { public int data; public Node next; }

C. class Node { public int data; Node next; }

D. public struct Node { int data; Node next; }

Solution

1. Step 1: Check for correct access modifiers and syntax

   public class Node { public int data; public Node next; } uses public for both data and next pointer, which is standard for node class fields.

2. Step 2: Verify class declaration and member types

   public class Node { public int data; public Node next; } correctly declares a class with an integer data and a pointer to the next node of the same type.

3. Final Answer:

   public class Node { public int data; public Node next; } -> Option B

4. Quick Check:

   Correct class with public members = public class Node { public int data; public Node next; } [OK]

Hint: Use public class with public fields for simple node design [OK]

Common Mistakes:

• Missing public keyword causing access issues
• Using struct instead of class for linked nodes
• Incorrect constructor syntax

3. Consider the following C# code for a singly linked list node and a small list creation:

public class Node {
  public int data;
  public Node next;
  public Node(int d) { data = d; next = null; }
}

Node head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);

Console.WriteLine(head.next.next.data);

What will be the output?

medium

A. 3

B. 2

C. NullReferenceException

D. 1

Solution

1. Step 1: Trace node creation and linking

   Head node has data 1, its next points to node with data 2, which in turn points to node with data 3.

2. Step 2: Access head.next.next.data

   This accesses the third node's data, which is 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Third node data = 3 [OK]

Hint: Follow next pointers step-by-step to find data [OK]

Common Mistakes:

• Confusing node positions and accessing wrong data
• Assuming next.next is null
• Expecting runtime error incorrectly

4. Given the following node class and code snippet, identify the error:

public class Node {
  public int data;
  public Node next;
  public Node(int d) { data = d; next = null; }
}

Node head = new Node(10);
head.next.next = new Node(20);

What is the problem here?

medium

A. Data type mismatch in node declaration

B. Node class is missing a constructor

C. No error, code runs fine

D. head.next is null, so accessing head.next.next causes an error

Solution

1. Step 1: Analyze the initial node creation

   Head node is created with data 10, and its next pointer is null by default.

2. Step 2: Check the assignment head.next.next = new Node(20);

   Since head.next is null, trying to access head.next.next causes a NullReferenceException.

3. Final Answer:

   head.next is null, so accessing head.next.next causes an error -> Option D

4. Quick Check:

   Null pointer access causes error [OK]

Hint: Always initialize intermediate nodes before accessing their pointers [OK]

Common Mistakes:

• Assuming next is auto-initialized
• Ignoring null pointer exceptions
• Thinking constructor is missing

5. You want to design a doubly linked list node in C# that can point both to the previous and next nodes. Which of the following class definitions correctly implements this?

hard

A. public class Node { public int data; public Node prev; public Node next; public Node(int d) { data = d; prev = null; next = null; } }

B. public class Node { int data; Node next; Node prev; public Node(int d) { data = d; next = null; } }

C. public class Node { public int data; public Node next; public Node(int d) { data = d; next = null; } }

D. public struct Node { public int data; public Node prev; public Node next; }

Solution

1. Step 1: Identify the need for both prev and next pointers

   A doubly linked list node must have pointers to both previous and next nodes to allow two-way traversal.

2. Step 2: Check class definition correctness

   public class Node { public int data; public Node prev; public Node next; public Node(int d) { data = d; prev = null; next = null; } } correctly declares public prev and next pointers and initializes them to null in the constructor.

3. Final Answer:

   public class Node { public int data; public Node prev; public Node next; public Node(int d) { data = d; prev = null; next = null; } } -> Option A

4. Quick Check:

   Doubly linked node has both prev and next pointers [OK]

Hint: Doubly linked nodes need both prev and next pointers [OK]

Common Mistakes:

• Omitting the prev pointer
• Using struct instead of class for nodes
• Not initializing pointers in constructor