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

Node Structure and Pointer Design

📖 Scenario: You are building a simple linked list to store numbers. Each item in the list is called a node. Each node holds a number and a pointer to the next node. This helps you connect nodes in a chain.

🎯 Goal: Create a node structure with a number and a pointer to the next node. Then create two nodes and link them together. Finally, print the values in the linked nodes.

📋 What You'll Learn

Create a struct called Node with an int data and a Node* next pointer

Create two Node variables called first and second

Set first.data to 10 and second.data to 20

Link first.next to &second and second.next to nullptr

Print the values of first.data and second.data by following the pointers

💡 Why This Matters

🌍 Real World

Linked lists are used in many programs to store and manage data dynamically, like playlists, undo history, or navigation paths.

💼 Career

Understanding node structures and pointers is essential for software developers working with low-level data structures, memory management, and performance optimization.

1

Create the Node structure

Create a struct called Node with two members: an int data and a Node* next pointer.

DSA C++

// Your code here

Hint

Think of Node as a box holding a number and a pointer to the next box.

2

Create two nodes and assign data

Create two Node variables called first and second. Set first.data to 10 and second.data to 20.

DSA C++

struct Node {
    int data;
    Node* next;
};

// Your code here

Hint

Make two boxes and put 10 in the first and 20 in the second.

3

Link the nodes

Set first.next to point to &second and second.next to nullptr to mark the end of the list.

DSA C++

struct Node {
    int data;
    Node* next;
};

Node first;
Node second;
first.data = 10;
second.data = 20;

// Your code here

Hint

Link the first box to the second, and the second box points to nothing.

4

Print the linked nodes' data

Print the values of first.data and second.data by following the pointers. Use std::cout to print first.data and then first.next->data separated by a space.

DSA C++

struct Node {
    int data;
    Node* next;
};

Node first;
Node second;
first.data = 10;
second.data = 20;
first.next = &second;
second.next = nullptr;

// Your code here

Hint

Use std::cout to print the first node's data and then the second node's data by following the pointer.

Practice

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

easy

A. To store the data value of the node

B. To keep track of the size of the list

C. To point to the previous node in the list

D. To store the address of the next node in 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.

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

   The next pointer stores the address of the next node, allowing traversal through the list.

3. Final Answer:

   To store the address of the next node in the list -> Option D

4. Quick Check:

   next pointer = address of next node [OK]

Hint: Next pointer always links to the next node in the chain [OK]

Common Mistakes:

• Confusing data storage with pointer storage
• Thinking next points to previous node
• Assuming next stores list size

2. Which of the following is the correct syntax to define a node structure with an integer data and a pointer to the next node in C++?

easy

A. struct Node { int data; Node* next; };

B. struct Node { int data; next Node*; };

C. struct Node { int data; *Node next; };

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

Solution

1. Step 1: Recall pointer declaration syntax in C++

   To declare a pointer to a type, use the syntax TypeName* pointerName;.

2. Step 2: Check each option for correct pointer syntax

   struct Node { int data; Node* next; }; correctly declares Node* next; as a pointer to a Node. Others have syntax errors.

3. Final Answer:

   struct Node { int data; Node* next; }; -> Option A

4. Quick Check:

   Pointer syntax = TypeName* [OK]

Hint: Pointer syntax always uses * after type name [OK]

Common Mistakes:

• Omitting the * for pointer declaration
• Placing * before variable name incorrectly
• Using variable name before type

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

struct Node {
  int data;
  Node* next;
};

int main() {
  Node a = {10, nullptr};
  Node b = {20, nullptr};
  a.next = &b;
  std::cout << a.next->data << std::endl;
  return 0;
}

medium

A. 20

B. 10

C. Address of b

D. Compilation error

Solution

1. Step 1: Understand the node initialization and linking

   Node a has data 10 and next initially null. Node b has data 20. Then a.next points to b.

2. Step 2: Trace the output statement

   a.next->data accesses the data of the node pointed by a.next, which is b with value 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   Pointer access a.next->data = 20 [OK]

Hint: Arrow operator accesses member via pointer [OK]

Common Mistakes:

• Printing a.data instead of a.next->data
• Confusing pointer dereference syntax
• Expecting address instead of data

4. Identify the error in the following node structure code snippet:

struct Node {
  int data;
  Node next;
};

medium

A. Missing semicolon after struct definition

B. Data member should be a pointer

C. Pointer to next node should be declared as Node* next;

D. Struct cannot contain another struct

Solution

1. Step 1: Analyze the declaration of next member

   The member next is declared as Node next;, which means it contains a full Node inside itself, causing infinite size.

2. Step 2: Correct pointer declaration

   To link nodes, next must be a pointer: Node* next; to store address of another node.

3. Final Answer:

   Pointer to next node should be declared as Node* next; -> Option C

4. Quick Check:

   Next node must be pointer type [OK]

Hint: Next node must be pointer, not full struct [OK]

Common Mistakes:

• Declaring next as full struct causes infinite recursion
• Forgetting * in pointer declaration
• Confusing pointer and object types

5. You want to design a doubly linked list node structure in C++ that stores an integer and has pointers to both previous and next nodes. Which of the following is the correct definition?

hard

A. struct Node { int data; Node prev; Node next; };

B. struct Node { int data; Node* prev; Node* next; };

C. struct Node { int data; Node* prev; Node next; };

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

Solution

1. Step 1: Understand doubly linked list node requirements

   Each node must have data and two pointers: one to previous node and one to next node.

2. Step 2: Check pointer declarations for both prev and next

   Both prev and next must be pointers to Node, declared as Node* prev; and Node* next;.

3. Final Answer:

   struct Node { int data; Node* prev; Node* next; }; -> Option B

4. Quick Check:

   Both prev and next are pointers [OK]

Hint: Both prev and next must be pointers in doubly linked list [OK]

Common Mistakes:

• Declaring prev or next as full Node instead of pointer
• Mixing pointer and non-pointer types
• Forgetting one of the pointers