The following function reverse() is supposed to reverse a singly linked list. There is one line missing at the end of the function.

/* Link list node */ struct node { int data; struct node* next; }; /* head_ref is a double pointer which points to head (or start) pointer of linked list */ static void reverse(struct node** head_ref) { struct node* prev = NULL; struct node* current = *head_ref; struct node* next; while (current != NULL) { next = current->next; current->next = prev; prev = current; current = next; } /*ADD A STATEMENT HERE*/ }

What should be added in place of “/*ADD A STATEMENT HERE*/”, so that the function correctly reverses a linked list.

**(A)** *head_ref = prev;

**(B)** *head_ref = current;

**(C)** *head_ref = next;

**(D)** *head_ref = NULL;

**Answer:** **(A)** **Explanation:** *head_ref = prev;

At the end of while loop, the *prev *pointer points to the last node of original linked list. We need to change *head_ref so that the head pointer now starts pointing to the last node.

See the following complete running program.

#include<stdio.h> #include<stdlib.h> /* Link list node */ struct node { int data; struct node* next; }; /* Function to reverse the linked list */ static void reverse(struct node** head_ref) { struct node* prev = NULL; struct node* current = *head_ref; struct node* next; while (current != NULL) { next = current->next; current->next = prev; prev = current; current = next; } *head_ref = prev; } /* Function to push a node */ void push(struct node** head_ref, int new_data) { /* allocate node */ struct node* new_node = (struct node*) malloc(sizeof(struct node)); /* put in the data */ new_node->data = new_data; /* link the old list off the new node */ new_node->next = (*head_ref); /* move the head to point to the new node */ (*head_ref) = new_node; } /* Function to print linked list */ void printList(struct node *head) { struct node *temp = head; while(temp != NULL) { printf("%d ", temp->data); temp = temp->next; } } /* Drier program to test above function*/ int main() { /* Start with the empty list */ struct node* head = NULL; push(&head, 20); push(&head, 4); push(&head, 15); push(&head, 85); printList(head); reverse(&head); printf("\n Reversed Linked list \n"); printList(head); return 0; }

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