Node Structure and Pointer Design in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a pointer to the next node in a singly linked list node structure.

DSA C++

struct Node {
    int data;
    Node* [1];
};

Drag options to blanks, or click blank then click option'

Alink

Bnext

Cprev

Dpointer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists.

Using generic names like 'pointer' which are unclear.

The pointer to the next node in a singly linked list is conventionally named 'next'.

2fill in blank

medium

Complete the constructor initialization list to set the data value in the node.

DSA C++

struct Node {
    int data;
    Node* next;
    Node(int val) : data([1]), next(nullptr) {}
};

Drag options to blanks, or click blank then click option'

Anext

Bvalue

Cdata

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'data' instead of 'val' in initialization.

Using 'next' or 'value' which are incorrect here.

The constructor parameter 'val' is used to initialize the 'data' member.

3fill in blank

hard

Fix the error in the pointer assignment to link two nodes.

DSA C++

Node* first = new Node(10);
Node* second = new Node(20);
first->[1] = second;

Drag options to blanks, or click blank then click option'

Anext

Bpointer

Clink

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists.

Using undefined pointer names like 'link' or 'pointer'.

To link nodes in a singly linked list, assign the 'next' pointer of the first node to the second node.

4fill in blank

hard

Fill both blanks to complete the function that creates a new node and returns its pointer.

DSA C++

Node* createNode(int val) {
    Node* newNode = new Node([1]);
    newNode->[2] = nullptr;
    return newNode;
}

Drag options to blanks, or click blank then click option'

Aval

Bnext

Cprev

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'data' instead of 'val' in constructor.

Setting 'prev' pointer which does not exist in singly linked list.

The new node is created with 'val' and its 'next' pointer is set to nullptr.

5fill in blank

hard

Fill all three blanks to complete the function that inserts a new node at the beginning of the list.

DSA C++

void insertAtHead(Node*& head, int val) {
    Node* newNode = new Node([1]);
    newNode->[2] = head;
    head = [3];
}

Drag options to blanks, or click blank then click option'

Aval

Bnext

CnewNode

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head to newNode->next instead of the other way.

Not updating head pointer after insertion.

Create new node with 'val', set its 'next' to current head, then update head to newNode.

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