C Program of Double Linked List

#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()*/