Delete Node at Beginning in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the head pointer to the next node after deletion.

DSA C

head = [1];

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

ANULL

Bhead->prev

Chead->next

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Setting head to NULL instead of head->next

Using head->prev which points backward

Not updating head at all

After deleting the first node, the head should point to the next node in the list.

2fill in blank

medium

Complete the code to free the memory of the deleted node.

DSA C

struct Node* temp = head;
head = head->next;
[1](temp);

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

Adelete

Bfree

Cremove

Ddispose

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete which is C++ keyword

Using remove or dispose which are not valid in C

Not freeing memory causing memory leaks

In C, free() is used to release memory allocated with malloc().

3fill in blank

hard

Fix the error in the condition to check if the list is empty before deletion.

DSA C

if ([1] == NULL) {
    printf("List is empty\n");
    return;
}

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

Ahead->prev

Bhead->next

Ctemp

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Checking head->next which causes segmentation fault if head is NULL

Checking temp which may not be initialized

Checking head->prev which is irrelevant for singly linked list

To check if the list is empty, we check if the head pointer itself is NULL.

4fill in blank

hard

Fill both blanks to correctly delete the first node and update the head.

DSA C

if (head == NULL) {
    printf("List is empty\n");
    return;
}
struct Node* [1] = head;
head = [2];
free(temp);

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

Atemp

Bhead->next

Chead

Dtemp->next

Attempts:

3 left

💡 Hint

Common Mistakes

Not using a temporary pointer causing loss of reference

Freeing head before updating it

Assigning head to temp instead of temp to head

We store the current head in temp, then move head to the next node before freeing temp.

5fill in blank

hard

Fill all three blanks to implement a function that deletes the first node of a singly linked list.

DSA C

void deleteAtBeginning(struct Node** [1]) {
    if (*[1] == NULL) {
        printf("List is empty\n");
        return;
    }
    struct Node* temp = *[1];
    *[2] = (*[3])->next;
    free(temp);
}

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

Ahead

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Using single pointer instead of double pointer for head

Not dereferencing head correctly

Freeing memory before updating head

The function takes a pointer to the head pointer. We check if the list is empty by dereferencing *head. Then we update *head to point to the next node before freeing the old head.

Practice

1. What happens to the linked list when you delete the node at the beginning?

easy

A. All nodes are deleted at once.

B. The last node is deleted instead of the first.

C. The list remains unchanged.

D. The head pointer moves to the next node, removing the first node.

Solution

1. Step 1: Understand the head pointer role

   The head pointer points to the first node in the linked list.

2. Step 2: Effect of deleting the first node

   Deleting the first node means moving the head pointer to the second node, effectively removing the first node from the list.

3. Final Answer:

   The head pointer moves to the next node, removing the first node. -> Option D

4. Quick Check:

   Deleting at beginning means head moves forward [OK]

Hint: Deleting at start moves head to next node [OK]

Common Mistakes:

• Thinking the last node is deleted
• Assuming the list stays the same
• Deleting all nodes instead of one

2. Which of the following is the correct syntax to delete the first node in a singly linked list in C?

easy

A. temp = head; head = head->next; free(temp);

B. head = head->next; free(head);

C. free(head); head = head->next;

D. head->next = NULL; free(head);

Solution

1. Step 1: Store current head in temp

   We save the current head node in a temporary pointer to free it later.

2. Step 2: Move head to next node and free old head

   Update head to point to the next node, then free the old head stored in temp.

3. Final Answer:

   temp = head; head = head->next; free(temp); -> Option A

4. Quick Check:

   Save old head, move head, free old [OK]

Hint: Save old head before moving and freeing [OK]

Common Mistakes:

• Freeing head before moving pointer
• Not saving old head before moving
• Setting next to NULL incorrectly

3. What will be the output linked list after deleting the first node from the list: 10 -> 20 -> 30 -> NULL?

medium

A. 10 -> 20 -> 30 -> NULL

B. NULL

C. 20 -> 30 -> NULL

D. 30 -> NULL

Solution

1. Step 1: Identify the first node

   The first node has value 10.

2. Step 2: Delete first node and move head

   After deletion, head points to node with value 20, so list starts from 20.

3. Final Answer:

   20 -> 30 -> NULL -> Option C

4. Quick Check:

   First node removed, next node becomes head [OK]

Hint: After deletion, list starts from second node [OK]

Common Mistakes:

• Not updating head pointer
• Deleting wrong node
• Assuming list becomes empty

4. Consider this code snippet to delete the first node:

struct Node* temp = head;
head = head->next;
free(head);

What is the error in this code?

medium

A. It frees the new head instead of the old head.

B. It does not update the head pointer.

C. It frees the temp pointer instead of head.

D. It causes a syntax error.

Solution

1. Step 1: Analyze pointer usage

   temp stores old head, head moves to next node.

2. Step 2: Identify which node is freed

   free(head) frees the new head, not the old node stored in temp, causing memory error.

3. Final Answer:

   It frees the new head instead of the old head. -> Option A

4. Quick Check:

   Free old node, not new head [OK]

Hint: Free the saved old head pointer, not the updated head [OK]

Common Mistakes:

• Freeing updated head instead of old node
• Not freeing any node causing memory leak
• Confusing temp and head pointers

5. You have a singly linked list with nodes: 5 -> 15 -> 25 -> 35 -> NULL. After deleting the first node twice, what will be the resulting list?

hard

A. 15 -> 25 -> 35 -> NULL

B. 25 -> 35 -> NULL

C. 35 -> NULL

D. NULL

Solution

1. Step 1: Delete first node once

   First deletion removes 5, list becomes 15 -> 25 -> 35 -> NULL.

2. Step 2: Delete first node again

   Second deletion removes 15, list becomes 25 -> 35 -> NULL.

3. Final Answer:

   25 -> 35 -> NULL -> Option B

4. Quick Check:

   Two deletions remove first two nodes [OK]

Hint: Each deletion moves head forward by one node [OK]

Common Mistakes:

• Deleting only once instead of twice
• Confusing node values after deletion
• Assuming list becomes empty too soon