C program of Double Linked List

/*Write a C program that uses functions to perform the following operations on Doubly linked list:
i) Creation
ii)Insertion
iii)Deletion
iv)Traversal in both ways */
#include <stdio.h>
#include <malloc.h>

struct node
{
  struct node *prev;
  int info;
  struct node *next;
}*start;

main()
{
  int choice,n,m,po,i;
  start=NULL;
  while(1)
  {
    printf("1.Create List\n");
    printf("2.Add at begining\n");
    printf("3.Add after\n");
    printf("4.Delete\n");
    printf("5.Display\n");
    printf("6.Count\n");
    printf("7.Reverse\n");
    printf("8.exit\n");
    printf("Enter your choice : ");
    scanf("%d",&choice);
    switch(choice)
    {
     case 1: printf("How many nodes you want : ");
         scanf("%d",&n);
          for(i=0;i<n;i++)
          {
        printf("Enter the element : ");
        scanf("%d",&m);
        create_list(m);
          }
          break;
    case 2:    printf("Enter the element : ");
        scanf("%d",&m);
        addatbeg(m);
        break;
    case 3: printf("Enter the element : ");
        scanf("%d",&m);
        printf("Enter the position after which this element is inserted : ");
        scanf("%d",&po);
        addafter(m,po);
        break;
    case 4:    printf("Enter the element for deletion : ");
        scanf("%d",&m);
        del(m);
        break;
    case 5:    display();
        break;
    case 6: count();
        break;
    case 7: rev();
        break;
    case 8: exit();
    default:printf("Wrong choice\n");
    }/*End of switch*/
  }/*End of while*/
}/*End of main()*/

create_list(int num)
{
    struct node *q,*tmp;
    tmp= malloc(sizeof(struct node));
    tmp->info=num;
    tmp->next=NULL;
    if(start==NULL)
    {
        tmp->prev=NULL;
        start->prev=tmp;
        start=tmp;
    }
    else
    {
        q=start;
        while(q->next!=NULL)
          q=q->next;
        q->next=tmp;
        tmp->prev=q;
    }
}/*End of create_list()*/

addatbeg(int num)
{
  struct node *tmp;
  tmp=malloc(sizeof(struct node));
  tmp->prev=NULL;
  tmp->info=num;
  tmp->next=start;
  start->prev=tmp;
  start=tmp;
}/*End of addatbeg()*/

addafter(int num,int c)
{
  struct node *tmp,*q;
  int i;
  q=start;
  for(i=0;i<c-1;i++)
  {
    q=q->next;
    if(q==NULL)
    {
      printf("There are less than %d elements\n",c);
      return;
    }
  }
  tmp=malloc(sizeof(struct node) );
  tmp->info=num;
  q->next->prev=tmp;
  tmp->next=q->next;
  tmp->prev=q;
  q->next=tmp;
}/*End of addafter() */

del(int num)
{
  struct node *tmp,*q;
  if(start->info==num)
  {
    tmp=start;
    start=start->next;  /*first element deleted*/
    start->prev = NULL;
    free(tmp);
    return;
  }
  q=start;
  while(q->next->next!=NULL)
  {
    if(q->next->info==num)     /*Element deleted in between*/
    {
      tmp=q->next;
      q->next=tmp->next;
      tmp->next->prev=q;
      free(tmp);
      return;
    }
    q=q->next;
  }
  if(q->next->info==num)    /*last element deleted*/
  {   tmp=q->next;
    free(tmp);
    q->next=NULL;
    return;
  }
  printf("Element %d not found\n",num);
}/*End of del()*/

display()
{
  struct node *q;
  if(start==NULL)
  {
    printf("List is empty\n");
    return;
  }
  q=start;
  printf("List is :\n");
  while(q!=NULL)
  {
    printf("%d ", q->info);
    q=q->next;
  }
  printf("\n");
}/*End of display() */

count()
{   struct node *q=start;
  int cnt=0;
  while(q!=NULL)
  {
    q=q->next;
    cnt++;
  }
  printf("Number of elements are %d\n",cnt);
}/*End of count()*/

rev()
{
  struct node *p1,*p2;
  p1=start;
  p2=p1->next;
  p1->next=NULL;
  p1->prev=p2;
  while(p2!=NULL)
  {
    p2->prev=p2->next;
    p2->next=p1;
    p1=p2;
    p2=p2->prev; /*next of p2 changed to prev */
  }
  start=p1;
}/*End of rev()*/

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