Doubly Linked List: Delete from Front

Doubly Linked List: Delete from Front

#include<stdio.h>

#include<stdlib.h>

struct node

{

            int data;

            struct node *llink;

            struct node *rlink;

};

typedef struct node* NODE;

NODE getnode();

void display(NODE first);

NODE insert_at_front(NODE first, int item);

NODE delete_at_front(NODE first);

NODE getnode()

{

            NODE x;

            x = (NODE) malloc(sizeof(struct node));

            x->llink = NULL;

            x->rlink = NULL;

            return x;

}

void display(NODE first)

{

            NODE cur;

            cur = first;

            printf("\nContents are:");

            if(cur == NULL)

                        printf("\nList is empty. Nothing to display.");

            else

            {

                        while(cur!=NULL)

                        {

                                    printf("%d  ", cur->data);

                                    cur = cur->rlink;

                        }

            }

}

NODE insert_at_front(NODE first, int item)

{

            int val;

            NODE temp;

            temp = getnode();

            temp->data = item;

           

            if(first == NULL)

            {

                                    return temp;

            }

            temp->rlink = first;

            first->llink = temp;

            return temp;

}

NODE delete_at_front(NODE first)

{

            NODE temp;

            if(first == NULL)                         /*Case 1: List is empty*/

            {

                        printf("\nList is empty. Cannot delete.");

                        return NULL;

            }

             

            /*Case 2: List has only one node*/

            if(first->rlink == NULL) 

            {

                        printf("\nItem that got deleted is %d", first->data);

                        free(first);

                        return NULL;

            }

         

            /*Case 3: List is not empty*/

            temp = first;                                                  

            first = first->rlink;

            first->llink = NULL;

            printf("\nItem that got deleted is %d", temp->data);

            free(temp);

            return first;

}

void main()

{

            int ch, item;

            NODE first = NULL;

            while(1)

            {

                        printf("\n\n~~MENU~~");

                        printf("\n1.Insert at front");

                        printf("\n2.Delete from front");

                        printf("\n3.Display");

                        printf("\n4.exit");

                        printf("\nEnter your choice: ");

                        scanf("%d", &ch);

                        switch(ch)

                        {

                                    case 1:     printf("\nEnter the value: ");

                                                    scanf("%d", &item);

                                                    first = insert_at_front(first, item);

                                                    break;

                                     case 2:    first = delete_at_front(first);

                                                    break;

                                     case 3:    display(first);

                                                    break;

                                     case 4:    exit(0);

                        }

            }

}

Output:

~~MENU~~

1.Insert at front

2.Delete from front

3.Display

4.exit

Enter your choice: 1

Enter the value: 11

~~MENU~~

1.Insert at front

2.Delete from front

3.Display

4.exit

Enter your choice: 1

Enter the value: 12

~~MENU~~

1.Insert at front

2.Delete from front

3.Display

4.exit

Enter your choice: 3

Contents are:12         11

~~MENU~~

1.Insert at front

2.Delete from front

3.Display

4.exit

Enter your choice: 2

Item that got deleted is 12

~~MENU~~

1.Insert at front

2.Delete from front

3.Display

4.exit

Enter your choice: 2

Item that got deleted is 11

~~MENU~~

1.Insert at front

2.Delete from front

3.Display

4.exit

Enter your choice: 2

List is empty. Cannot delete.