DLLques2.c

/*1. Create a DLL(DOUBLE LINKED LIST)
2. Enter 5 positive number in ascending order
3. Create a function which takes this DLL as argument and create another DLL which is reverse of the previous DLL.
4. Print the reverse DLL in main to show that function is working properly
5. Concatenate both link list in order where the 1st comes after 2nd.*/




#include<stdio.h>

typedef struct node{                   // doubly linked node
    int info;
    struct Node* next;         // points to next node
    struct Node* prev;     // points to previous node
}node;

node * addtoempty(node * start, int n)
{
    node * tmp;
    tmp = (node *)malloc(sizeof(node));
    tmp->info = n;
    tmp->prev = NULL;
    tmp->next = NULL;
    start = tmp;
    return start;
}//end of addtoempty

node * addtoend(node * start, int data)
{
    node * tmp, *ptr;
    tmp = (node *)malloc(sizeof(node));
    tmp->info = data;
    ptr=start; //now we have to traverse to find the end location
    while(ptr->next != NULL)
        ptr = ptr->next;
    ptr->next=tmp;
    tmp->prev=ptr;
    tmp->next=NULL;
    return start;
}//end of addtoend
node * createlist(node * start, int data)
{
    if (start == NULL)
        {
            start = addtoempty(start,data);
            return start;

        }
    else
        {
            start = addtoend(start,data);
            return start;
        }
}//end of create_list

node * rev_dll(node* start)
    {
        int i;
        node * p1,*p2=NULL;
        p1 = start;

        while(p1->next!=NULL)
            p1 = p1->next;

        //p2=p1;
        for(i=1;i<=5;i++)
            {
                    p2 = createlist(p2,p1->info);
                    p1 = p1->prev;

            }

        return p2;
    }//end of rev_dll

node * concatenate_list(node *rev_start,node *start)
    {   node * start1;

        if(rev_start == NULL)
            {
                rev_start = start;
                return rev_start;
            }
        if(start == NULL)
            return rev_start;
        start1 = rev_start;
        while(start1->next!= NULL)
            start1 = start1->next;
        start1->next = start;
        return rev_start;


    }//end of concatenate_list
void display(node * start)
{
    node * ptr;
    ptr = start;
    while(ptr!=NULL)
        {
            printf("%3d ",ptr->info);
            ptr = ptr->next;
        }
}//end of display




int main()
{   node * start=NULL,*rev_start,*con_start;



    int i,data;
    printf("Please enter 5 positive number in ascending order: \n");

    for ( i = 1; i <= 5; i++)
    {
        printf("Enter the nuber %d:  \n",i);
        scanf("%d",&data);
        start = createlist(start,data);
    }
    printf("\nHere is your list:  \n");
    display(start);
   printf("\n Here is the reversed list:  \n");
   rev_start = rev_dll(start);
    display(rev_start);
    printf("\nHere is the merged list (first list after second): \n");
    con_start = concatenate_list(rev_start,start);


    display(con_start);

    return 0;
}