DOUBLY LINKED LIST

#include<stdio.h>
#include<conio.h>


struct node
{
int info;
struct node *flink;
struct node *blink;
};


struct node* creation();
void display(struct node*);
struct node* insfirst(struct node*);
struct node* inslast(struct node*);



struct node* insele(struct node*);
struct node* inspos(struct node*);
struct node* delfirst(struct node*);
struct node* dellast(struct node*);
struct node* delele(struct node*);
struct node* delpos(struct node*);


void main()
{
int choice,ch;
struct node *head=NULL;
clrscr();
do
{
 printf("\n\n\n\t\t\tPGM FOR DOUBLY LINKED LIST\nenter your choice\n");
 printf("\n\n1.creation\n2.viewing\n3.insertion\n4.deletion\n5.exit from the program\n\n");
 scanf("%d",&choice);
  switch(choice)
 {
  case 1:printf("\n\t\t\tcreation of doubly linked list\n");
head=creation();
display(head);
break;
  case 2:display(head);
break;
  case 3:printf("\n\n\t\tinsertion in doubly linked list\n");
printf("\n\n\tenter your choice\n1.insertion at first node\n2.insertion at last\n3.insertion by element\n4.insertion by position\n\n");
scanf("%d",&ch);
switch(ch)
{
 case 1:printf("\n\tinsertion at head node\n");
head=insfirst(head);
break;
 case 2:printf("\n\tinsertion at last\n");
head=inslast(head);
break;
 case 3:printf("\n\tinsertion by element\n");
head=insele(head);
break;
 case 4:printf("\n\tinsertion by position\n");
head=inspos(head);
break;
 default:printf("\n\tinvalid entry\n");
};
break;
  case 4:if(head!=NULL)
{
 printf("\n\n\tdeletion of a node\nenter your choice\n");
 printf("\n1.del at first\n2.del at last\n3.del by element\n4.del by position");
 scanf("%d",&ch);
 switch(ch)
 {
  case 1:printf("\n\tdeletion at head node\n");
 head=delfirst(head);
 break;
  case 2:printf("\n\tdeletion at last\n");
 head=dellast(head);
 break;
  case 3:printf("\n\tinsertion by element\n");
 head=delele(head);
 break;
  case 4:printf("\n\tinsertion by position\n");
 head=delpos(head);
 break;
  default:printf("\n\tinvalid entry\n");
 };
}
else
printf("\ndeletion not possible\nlist is empty\n");
break;
  case 5:printf("\n\n\tThankyou");
getch();
break;
  default:printf("\n\ninvalid entry");


 };
}while(choice!=5);
}


struct node* creation()
{
 int n,i;
 struct node *first,*temp,*newnode;
 first->blink=NULL;
 first->flink=NULL;
 printf("\nenter the number of nodes to be created\n");
 scanf("%d",&n);
 first=(struct node*)malloc(sizeof(struct node));
 printf("\nenter the data for node 1:");
 scanf("%d",&(first->info));
 temp=first;
 if(n>1)
 {
 for(i=1;i<n;i++)
 {
  struct node *newnode=(struct node*)malloc(sizeof(struct node));
  printf("\nenter the data for node %d:",i+1);
  scanf("%d",&(newnode->info));
  newnode->blink=temp;
  newnode->flink=NULL;
  temp->flink=newnode;
  temp=newnode;
  if(i==1)
   first->flink=temp;


 }
 }
 return(first);
}




void display(struct node *head)
{
 struct node *travel;
 if(head==NULL)
  printf("\n\nlist is empty\n");
 printf("\n\n\n\n\n");
 travel=head;
 printf("<---%u:%d:%u--->",travel->blink,travel->info,travel->flink);
 travel=travel->flink;
while(travel!=NULL)
 {
  printf("<---%u:%d:%u--->",travel->blink,travel->info,travel->flink);
  travel=travel->flink;
 }


}


struct node* insfirst(struct node *head)
{
 struct node *newnode;
 newnode=(struct node*)malloc(sizeof(struct node*));
 printf("\nenter the data to be inserted at head node\n");
 scanf("%d",&(newnode->info));
 newnode->blink=NULL;
 newnode->flink=head;
 head->blink=newnode;
 head=newnode;
 display(head);
 return(head);
}


struct node* inslast(struct node *head)
{
 struct node *newnode,*travel;
 newnode=(struct node*)malloc(sizeof(struct node));
 travel=head;
 printf("\nenter the data to be inserted at last\n");
 scanf("%d",&(newnode->info));
 newnode->flink=NULL;
 while(travel->flink!=NULL)
  travel=travel->flink;
 newnode->blink=travel;
 travel->flink=newnode;
 display(head);
 return(head);
}


struct node* insele(struct node *head)
{
 struct node *new,*travel,*next;
 int ele;
 travel=head;
 new=(struct node*)malloc(sizeof(struct node));
 printf("\ndisplaying list\n");
 display(head);
 printf("\nenter the data value after which element is to be inserted");
 scanf("%d",&ele);
 while(travel->flink!=NULL)
 {
  if(travel->info==ele)
  {
   printf("\nenter the data to be inserted\n");
   scanf("%d",&(new->info));
   next=travel->flink;
   new->blink=travel;
   new->flink=travel->flink;
   travel->flink=new;
   next->blink=new;
   display(head);
   return(head);
  }
  else
  travel=travel->flink;
 }
 printf("\nelement not found\n");
 return(head);
}


struct node* inspos(struct node *head)
{
struct node *new,*travel,*next;
int n,i;
i=1;
new=(struct node*)malloc(sizeof(struct node));
while(travel->flink!=NULL)
{
 travel=travel->flink;
 i++;
}
printf("\nenter the positon after which insertion is to be made\n(b/w1and%d)",i);
scanf("%d",&n);
if(n<i)
{
 printf("\nenter the data to be inserted\n");
 scanf("%d",&(new->info));
 i=1;
 travel=head;
 while(i<n)
 {
  travel=travel->flink;
  i++;
 }
 new->blink=travel;
 new->flink=travel->flink;
 next=travel->flink;
 next->blink=new;
 travel->flink=new;
 display(head);
 return(head);
}
else
printf("\ninvalid entry\n");
return(head);
}


struct node* delfirst(struct node *head)
{
  struct node *last,*prev;
 if(head->flink==NULL)
  {printf("\nthe data being deleted is %d\n",head->info);
   head=NULL;
   return(head);
  }
  printf("\nthe data being deleted is %d\n",head->info);
  head=head->flink;
  head->blink=NULL;
  display(head);
  return(head);
}


struct node* dellast(struct node *head)
{
struct node *last,*prev;
if(head->flink==NULL)
{
 printf("\nthe element being deleted is %d\n",head->info);
 head=NULL;
 display(head);
 return(head);
}
last=head;
while(last->flink!=NULL)
   last=last->flink;
  prev=last->blink;
  prev->flink=NULL;
printf("\n the element being deleted is %d\n",last->info);
display(head);
return(head);
}


struct node* delele(struct node *head)
{
struct node *travel,*prev;
int deldata;
travel=head;
printf("\nenter the element to be deleted\n");
scanf("%d",&deldata);
while(travel->flink!=NULL)
{
if(travel->info==deldata)
{
 prev=travel->blink;
 prev->flink=travel->flink;
 travel=travel->flink;
 travel->blink=prev;
 printf("\n\nthe deleted data is %d",deldata);
 display(head);
 return(head);
}
else
travel=travel->flink;
}
display(head);
return(head);
}


struct node* delpos(struct node *head)
{
struct node *travel,*prev;
  int count,pos;
  count=1;
  prev=head;
  while(travel->flink!=NULL)
  {
   count++;
   travel=travel->flink;
  }
  travel=head;
  printf("\nenter the positon of the node to be deletedb/w1 1 and %d\n",count);
  scanf("%d",&pos);
  if(pos<count)
  {
    count=1;
    while(count<=(pos-1))
    { prev=travel;
      travel=travel->flink;
      count++;
    }
    prev->flink=travel->flink;
    travel->blink=prev;
    printf("\nelement deleted sucessfully\n");
    display(head);
  }
  else
  printf("\ninvalid entry");
  return(head);
}