Circular Doubly Linked List: Insert at Front

Circular Doubly Linked List: Insert at 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);

void display(NODE last);

NODE getnode()

{

                NODE x;

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

                return x;

}

NODE insert_at_front(NODE last, int item)

{

                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;

}

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.Display");

                                printf("\n3.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:   display(last);

                                                              break;

                                                case 3:   exit(0);

                                }

                }

}

Output:

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 1

Enter the value: 11

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 2

Contents are:

| 70920 | 11 | 70920 |

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 1

Enter the value: 12

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 2

Contents are:

|70920 | 12 | 70920 | ==>  | 70944 | 11 | 70944 |

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 1

Enter the value: 13

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 2

Contents are:

|70920 | 13 | 70944 | ==>  |70968 | 12 | 70920 | ==> | 70944 | 11 | 70968 |

~~MENU~~

1.Insert at front

2.Display

3.exit

Enter your choice: 3