Double_LL.c

 #include<stdio.h>
#include<stdlib.h>

struct DNode
{
    int data;
    struct DNode *prev, *next;
};

struct DNode *start = NULL;

struct DNode *getnode()
{
    return ((struct DNode *)malloc(sizeof(struct DNode)));
}

void createList()
{
    start = getnode();
    start->prev = NULL;
    start->next = NULL;
    printf("\nEnter Data: ");
    scanf("%d", &start->data);
    struct DNode *q, *p;
    q = getnode();
    p = start;
    while(1)
    {
        int ch;
        printf("\nPress 1 - Continue and 0 - Exit: ");
        scanf("%d", &ch);
        if (ch == 1)
        {
            printf("\nEnter Data: ");
            scanf("%d", &q->data);
            q->next = NULL;
            q->prev = p;
            p->next = q;
            p = q;
        }
        else
            break;
    }
}

void insertBeg()
{
    struct DNode *q;
    q = getnode();
    printf("\nEnter element to insert at the beginning: ");
    scanf("%d", &q->data);
    q->next = start;
    q->prev = NULL;
    if (start != NULL)
    {
        start->prev = q;
    }
    start = q;
}

void insertEnd()
{
    struct DNode *q, *p;
    q = getnode();
    printf("\nEnter element to insert at the end: ");
    scanf("%d", &q->data);
    q->next = NULL;
    if (start == NULL)
    {
        q->prev = NULL;
        start = q;
    }
    else
    {
        p = start;
        while (p->next != NULL)
        {
            p = p->next;
        }
        q->prev = p;
        p->next = q;
    }
}

void insertNPos()
{
    struct DNode *p, *q;
    int pos;
    q = getnode();
    if (start == NULL)
    {
        printf("\nList is Empty\n");
        return;
    }
    printf("\nEnter the position where you want to insert: ");
    scanf("%d", &pos);
    if (pos < 1)
    {
        printf("\nInvalid Position\n");
        return;
    }
    if (pos == 1)
    {
        insertBeg();
        return;
    }
    p = start;
    for (int i = 1; i < pos-1 && p != NULL; i++)
    {
        p = p->next;
    }
    if (p == NULL)
    {
        printf("\nPosition does not Exists\n");
        return;
    }
    printf("Enter the element you want to insert: ");
    scanf("%d", &q->data);
    q->next = p->next;
    if (p->next != NULL)
    {
        p->next->prev = q;
    }
    q->prev = p;
    p->next = q;
}

void display()
{
    struct DNode *p;
    if (start == NULL)
    {
        printf("\nList is Empty\n");
        return;
    }
    p = start;
    printf("\nList Elements: ");
    while (p != NULL)
    {
        printf("%d ", p->data);
        p = p->next;
    }
    printf("\n");
}

int main()
{
    int choice;
    do
    {
        printf("\n1 - Create Double Linked List");
        printf("\n2 - Insert element from the begining");
        printf("\n3 - Insert element from the end");
        printf("\n4 - Insert element from the Nth Position");
        printf("\n5 - Delete element from the begining");
        printf("\n6 - Delete element from the end");
        printf("\n7 - Delete element from the Nth Position");
        printf("\n8 - Display Double Linked List");
        printf("\n9 - EXIT");

        printf("\nEnter your choice: ");
        scanf("%d", &choice);

        switch(choice)
        {
            case 1: createList();
                    break;
            case 2: insertBeg();
                    break;
            case 3: insertEnd();
                    break;
            case 4: insertNPos();
                    break;
//            case 5: deleteBeg();
//                    break;
//            case 6: deleteEnd();
//                    break;
//            case 7: deletePos();
//                    break;
            case 8: display();
                    break;
            case 9: exit(1);
            default: printf("\nINVALID CHOICE\n");
        }
    }while (choice != 0);
}