Circular Doubly Linked List: Delete from front

Circular 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();

NODE insert_at_front(NODE last, int item);

NODE delete_at_front(NODE last);

void display(NODE last);

NODE getnode()

{

        NODE x;

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

        return x;

}

NODE insert_at_front(NODE last, int item)

{

        int val;

        NODE temp;

        temp = getnode();

        temp->data = item;

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

        {

                last = temp;

        }

        else                                                                /*Case 2: If not empty*/

        {

                temp->rlink = last->rlink;

                last->rlink->llink = temp;

        }

        temp->llink = last;

        last->rlink = temp;

        return last;

}

NODE delete_at_front(NODE last)

{

        NODE temp;

        if(last == NULL)

        {

                printf("\n List is empty");

                return NULL;

        }

        if(last->rlink == last)

        {

                printf("\nThe node %d is deleted",last->data);

                free(last);

                return NULL;

        }

        temp = last->rlink;

        last->rlink = temp->rlink;

        last->rlink->llink = last;

        printf("\nThe node  %d is deleted",temp->data);

        free(temp);

        return last;

}

void display(NODE last)

{

        NODE cur;

        printf("\nContents are:\n");

        if(last == NULL)

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

        else

        {

                cur = last->rlink;

                while(cur != last)

                {

                        printf("|%d | %d | %d | ==>  ", cur->llink, cur->data, cur->rlink);

                        cur = cur->rlink;

                }

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

        }

}

void main()

{

        int ch, item;

        NODE last = NULL;

        while(1)

        {

            printf("\n\n~~MENU~~");

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

            printf("\n2.Delete at 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);

                                last = insert_at_front(last, item);

                                break;

                    case 2:     last = delete_at_front(last);

                                break;

                    case 3:     display(last);

                                break;

                    case 4: exit(0);

            }

        }

}

Output:

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 1

Enter the value: 11

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 1

Enter the value: 12

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 3

Contents are:

|5125192 | 12 | 5125192 | ==>  | 5125216 | 11 | 5125216 |

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 1

Enter the value: 14

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 3

Contents are:

|5125192 | 14 | 5125216 | ==>  |5125240 | 12 | 5125192 | ==>  | 5125216 | 11 | 5125240 |

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 2

The node  14 is deleted

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 2

The node  12 is deleted

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 2

The node 11 is deleted

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 2

List is empty

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 3

Contents are:

List is empty. Nothing to display.

~~MENU~~

1.Insert at front

2.Delete at front

3.Display

4.exit

Enter your choice: 4