Linked List vs Array When to Choose Which in DSA C - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers.

DSA C

int numbers[[1]];

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

A0

B10

C5

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero as size which creates an empty array.

Forgetting to specify the size.

The array size must be specified as 5 to hold 5 integers.

2fill in blank

medium

Complete the code to create a new node in a linked list.

DSA C

struct Node* newNode = (struct Node*) malloc(sizeof([1]));

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

ANode

Bstruct

Cint

Dmalloc

Attempts:

3 left

💡 Hint

Common Mistakes

Using sizeof(int) which is too small.

Using sizeof(struct) which is invalid.

We allocate memory for a Node structure, so sizeof(Node) is needed.

3fill in blank

hard

Fix the error in the code to correctly insert a node at the beginning of a linked list.

DSA C

newNode->next = [1];
head = newNode;

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

Anext

BnewNode

CNULL

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to newNode causes a cycle.

Setting next to NULL loses the rest of the list.

The new node's next should point to the current head before updating head.

4fill in blank

hard

Fill both blanks to complete the code that prints all elements of an integer array.

DSA C

for(int i = 0; i [1] n; i[2]) {
    printf("%d ", arr[i]);
}

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

A<

B<=

C++

D--

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes out-of-bounds access.

Using -- causes infinite loop.

The loop runs while i is less than n and increments i each time.

5fill in blank

hard

Fill all three blanks to complete the code that creates a linked list node and sets its data and next pointer.

DSA C

struct Node* node = (struct Node*) malloc(sizeof([1]));
node->data = [2];
node->next = [3];

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

ANode

Bvalue

CNULL

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using sizeof(int) instead of Node.

Forgetting to set next to NULL.

Allocate memory for Node, assign data from value, and set next to NULL for end of list.

Practice

1. Which data structure is better when you need fast random access to elements by index?

easy

A. Array

B. Linked List

C. Stack

D. Queue

Solution

1. Step 1: Understand random access in arrays

   Arrays store elements in contiguous memory, so accessing any element by index is fast and direct.

2. Step 2: Compare with linked list access

   Linked lists require traversal from the head to reach an element, making random access slower.

3. Final Answer:

   Array -> Option A

4. Quick Check:

   Random access = Array [OK]

Hint: For fast index access, choose arrays [OK]

Common Mistakes:

• Thinking linked lists provide fast random access
• Confusing stack or queue with random access
• Ignoring memory layout differences

2. Which of the following is the correct way to declare an array of 5 integers in C?

easy

A. int arr{};

B. int arr();

C. int arr[5];

D. int arr = new int[5];

Solution

1. Step 1: Recall C array declaration syntax

   In C, arrays are declared with type, name, and size in square brackets, like int arr[5];

2. Step 2: Check other options for errors

   int arr(); uses parentheses which is a function declaration, C uses braces which is invalid, D uses 'new' which is C++ syntax.

3. Final Answer:

   int arr[5]; -> Option C

4. Quick Check:

   C array declaration = int arr[5]; [OK]

Hint: Use square brackets for arrays in C [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using C++ 'new' keyword in C
• Using braces for array declaration

3. Consider the following C code snippet:

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

Node* head = NULL;

// Insert 3 nodes at the beginning
for (int i = 1; i <= 3; i++) {
  Node* newNode = (Node*)malloc(sizeof(Node));
  newNode->data = i;
  newNode->next = head;
  head = newNode;
}

// Print list
Node* temp = head;
while (temp != NULL) {
  printf("%d -> ", temp->data);
  temp = temp->next;
}
printf("NULL\n");

What is the printed output?

medium

A. 1 -> 2 -> 3 -> NULL

B. 3 -> 2 -> 1 -> NULL

C. NULL

D. 3 -> 1 -> 2 -> NULL

Solution

1. Step 1: Understand insertion at beginning in linked list

   Each new node is added at the head, so the last inserted node becomes the first in the list.

2. Step 2: Trace the loop values and list order

   Insert 1: list is 1 -> NULL Insert 2: list is 2 -> 1 -> NULL Insert 3: list is 3 -> 2 -> 1 -> NULL

3. Final Answer:

   3 -> 2 -> 1 -> NULL -> Option B

4. Quick Check:

   Insertion at head reverses order [OK]

Hint: Insertion at head reverses order [OK]

Common Mistakes:

• Assuming insertion appends at end
• Confusing order of nodes after insertion
• Ignoring pointer updates

4. The following code tries to insert a node at the end of a singly linked list but causes a runtime error. What is the error?

void insertEnd(Node** head, int val) {
  Node* newNode = (Node*)malloc(sizeof(Node));
  newNode->data = val;
  newNode->next = NULL;

  Node* temp = *head;
  while (temp->next != NULL) {
    temp = temp->next;
  }
  temp->next = newNode;
}

medium

A. Dereferencing NULL pointer when list is empty

B. Memory leak due to missing free()

C. Incorrect data assignment to newNode

D. Missing return statement in void function

Solution

1. Step 1: Analyze behavior when list is empty

   If *head is NULL, then temp = NULL. Accessing temp->next causes a runtime error (segmentation fault).

2. Step 2: Identify fix for empty list case

   Need to check if *head is NULL before loop and assign newNode as head if true.

3. Final Answer:

   Dereferencing NULL pointer when list is empty -> Option A

4. Quick Check:

   Empty list causes NULL pointer error [OK]

Hint: Check for empty list before traversal [OK]

Common Mistakes:

• Ignoring empty list case
• Confusing memory leak with pointer error
• Thinking missing return causes runtime error

5. You need to store a large number of elements where insertions and deletions happen frequently at random positions. Which data structure is more suitable and why? A) Array because it uses less memory B) Linked List because it allows efficient insertions and deletions C) Array because it provides faster random access D) Linked List because it uses contiguous memory

hard

A. Array because it uses less memory

B. Linked List because it uses contiguous memory

C. Array because it provides faster random access

D. Linked List because it allows efficient insertions and deletions

Solution

1. Step 1: Understand insertion and deletion costs

   Arrays require shifting elements for insertions/deletions at random positions, which is costly.

2. Step 2: Compare with linked list behavior

   Linked lists allow insertions and deletions by changing pointers without shifting elements, making them efficient for frequent changes.

3. Final Answer:

   Linked List because it allows efficient insertions and deletions -> Option D

4. Quick Check:

   Frequent insert/delete = Linked List [OK]

Hint: Frequent insert/delete? Choose linked list [OK]

Common Mistakes:

• Choosing array for frequent insertions
• Thinking linked list uses contiguous memory
• Ignoring cost of shifting in arrays