Question

Exercise: Delete First Element from a Linked List (pair)

This is a pair exercise to complete with your lab partner.

Download list_delete_first.c here, or copy it to your CSE account using the following command:

cp -n /web/dp1091/20T1/activities/list_delete_first/list_delete_first.c .

Your task is to add code to this function in list_delete_first.c:

//
// Delete the first node in list.
// The deleted node is freed.
// The head of the list is returned.
//
struct node *delete_first(struct node *head) {

    // PUT YOUR CODE HERE (change the next line!)
    return NULL;
}

Note list_delete_first.c uses the following familiar data type:

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

delete_first is given one argument, head, which is the pointer to the first node in the linked list.

Add code to delete_first so that it deletes the first node from list.

delete_first should return a pointer to the new first node in the list.

If the list is now empty delete_first should return NULL.

delete_first should call free to free the memory of the node it deletes.

For example if the linked list contains these 8 elements:

16, 7, 8, 12, 13, 19, 21, 12

delete_first should return a pointer to a list with these elements:

7, 8, 12, 13, 19, 21, 12

Hint: this is a simple task requiring only a few lines of code.

Testing

list_delete_first.c also contains a main function which allows you to test your delete_first function. It converts command-line arguments to a linked list, calls delete_first, and then prints the result.

Do not change this main function. If you want to change it, you have misread the question.

Your delete_first function will be called directly in marking. The main function is only to let you test your delete_first function

Here is how you the main function allows you to test delete_first:

cp -n /web/dp1091/20T1/activities/list_delete_first/list_delete_first.c .
dcc list_delete_first.c -o list_delete_first
./list_delete_first 16 7 8 12 13 19 21 12
[7, 8, 12, 13, 19, 21, 12]
./list_delete_first 2 4 6 2 4 6
[4, 6, 2, 4, 6]
./list_delete_first 42
[]
./list_delete_first
[]

Assumptions/Restrictions/Clarifications.

delete_first should call free to free the memory for the node it deletes

delete_first should not change the data fields of list nodes.

delete_first should not use arrays.

delete_first should not call malloc.

delete_first should not call scanf (or getchar or fgets).

delete_first should not print anything. It should not call printf.

Do not change the supplied main function. It will not be tested or marked.

New! You can run an automated code style checker using the following command:

~dp1091/bin/style list_delete_first.c

When you think your program is working you can use autotest to run some simple automated tests:

HERE IS THE STARTING CODE

https://shrib.com/#BlackVulture7DKWejX

Answer 1

• I have attached code and output screenshots for better understanding .Please go through it.

Note : while entering numbers through command line press -1 to stop.

// linked list.
#include <stdio.h>
#include<stdlib.h>

/* Link list node */
struct Node {
   int data;
   struct Node* next;
};

/* Function to remove the first node
of the linked list */
struct Node* delete_first(struct Node* head)
{
   if (head == NULL)
       return NULL;

   // Move the head pointer to the next node
   struct Node* temp = head;
   head = head->next;

   free(temp);

   return head;
}

// Function to insert node at last
void insert(struct Node** head_ref, int new_data)
{
   struct Node* new_node = (struct Node*)malloc(sizeof(struct node*));
   new_node->data = new_data;
   new_node->next = NULL;
   struct Node*temp=*head_ref;
   if((*head_ref)==NULL)
       *head_ref=new_node;
   else
   {
       while(temp->next!=NULL)
           temp=temp->next;
       temp->next=new_node;
   }
  

}

// Driver code
int main(int argc ,char* argv[])
{
   /* Start with the empty list */
   struct Node* head = NULL;   /* Use insert() function to construct
   the list*/
int i;
for (i=1;i<argc;i++)
{
   int val=atoi(argv[i]);

if (val == -1)
       break;
   insert(&head, val);
}

   head = delete_first(head);
   for (struct Node* temp = head; temp != NULL; temp = temp->next)
       printf(" %d",temp->data);

   return 0;
}