Doubly linked list

/*
Write a program for doubly linked list
*/

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

struct node

{

struct node *prev;

int info;

struct node *next;

};

struct node *create_list(struct node *start);

void display(struct node *start);

struct node *addtoempty(struct node *start,int data);

struct node *addatbeg(struct node *start,int data);

struct node *addatend(struct node *start,int data);

struct node *addafter(struct node *start,int data,int item);

struct node *addbefore(struct node *start,int data,int item);

struct node *del(struct node *start,int data);

struct node *reverse(struct node *start);

main()

{

int choice,data,item;

struct node *start=NULL;

while(1)

{

printf("1.Create List\n");

printf("2.Display\n");

printf("3.Add to empty list\n");

printf("4.Add at beginning\n");

printf("5.Add at end\n");

printf("6.Add after\n");

printf("7.Add before\n");

printf("8.Delete\n");

printf("9.Reverse\n");

printf("10.Quit\n");

printf("Enter your choice : ");

scanf("%d",&choice);

switch(choice)

{

case 1:

start=create_list(start);

break;

case 2:

display(start);

break;

case 3:

printf("Enter the element to be inserted : ");

scanf("%d",&data);

start=addtoempty(start,data);

break;

case 4:

printf("Enter the element to be inserted : ");

scanf("%d",&data);

start=addatbeg(start,data);

break;

case 5:

printf("Enter the element to be inserted : ");

scanf("%d",&data);

start=addatend(start,data);

break;

case 6:

printf("Enter the element to be inserted : ");

scanf("%d",&data);

printf("Enter the element after which to insert : ");

scanf("%d",&item);

start=addafter(start,data,item);

break;

case 7:

printf("Enter the element to be inserted : ");

scanf("%d",&data);

printf("Enter the element before which to insert : ");

scanf("%d",&item);

start=addbefore(start,data,item);

break;

case 8:

printf("Enter the element to be deleted : ");

scanf("%d",&data);

start=del(start,data);

break;

case 9:

start=reverse(start);

break;

case 10:

exit(1);

default:

printf("Wrong choice\n");

}
}
}

struct node *create_list(struct node *start)

{

int i,n,data;

printf("Enter the number of nodes : ");

scanf("%d",&n);

start=NULL;

if(n==0)

return start;

printf("Enter the element to be inserted : ");

scanf("%d",&data);

start=addtoempty(start,data);

for(i=2;i<=n;i++)

{

printf("Enter the element to be inserted : ");

scanf("%d",&data);

start=addatend(start,data);

}

return start;

}

void display(struct node *start)

{

struct node *p;

if(start==NULL)

{

printf("List is empty\n");

return;

}

p=start;

printf("List is :\n");

while(p!=NULL)

{

printf("%d ",p->info);

p=p->next;

}

printf("\n");

}

struct node *addtoempty(struct node *start,int data)

{

struct node *tmp;

tmp=(struct node *)malloc(sizeof(struct node));

tmp->info=data;

tmp->prev=NULL;

tmp->next=NULL;

start=tmp;

return start;

}

struct node *addatbeg(struct node *start,int data)

{

struct node *tmp;

tmp = (struct node *)malloc(sizeof(struct node));

tmp->info=data;

tmp->prev=NULL;

tmp->next=start;

start->prev=tmp;

start=tmp;

return start;

}

struct node *addatend(struct node *start,int data)

{

struct node *tmp,*p;

tmp=(struct node *)malloc(sizeof(struct node));

tmp->info=data;

p=start;

while(p->next!=NULL)

p=p->next;

p->next=tmp;

tmp->next=NULL;

tmp->prev=p;

return start;

}

struct node *addafter(struct node *start,int data,int item)

{

struct node *tmp,*p;

tmp=(struct node *)malloc(sizeof(struct node));

tmp->info=data;

p=start;

while(p!=NULL)

{

if(p->info==item)

{

tmp->prev=p;

tmp->next=p->next;

if(p->next!=NULL)

p->next->prev=tmp;

p->next=tmp;

return start;

}

p=p->next;

}

printf("%d not present in the list\n\n",item);

return start;

}


struct node *addbefore(struct node *start,int data,int item)

{

struct node *tmp,*q;

if(start==NULL )

{

printf("List is empty\n");

return start;

}

if(start->info==item)

{

tmp = (struct node *)malloc(sizeof(struct node));

tmp->info=data;

tmp->prev=NULL;

tmp->next=start;

start->prev=tmp;

start=tmp;

return start;

}

q=start;

while(q!=NULL)

{

if(q->info==item)

{

tmp=(struct node *)malloc(sizeof(struct node));

tmp->info=data;

tmp->prev=q->prev;

tmp->next = q;

q->prev->next=tmp;

q->prev=tmp;

return start;

}

q=q->next;

}

printf("%d not present in the list\n",item);

return start;

}


struct node *del(struct node *start,int data)

{

struct node *tmp;

if(start==NULL)

{

printf("List is empty\n");

return start;

}

if(start->next==NULL) /*only one node in the list*/

if(start->info==data)

{

tmp=start;

start=NULL;

free(tmp);

return start;

}

else

{

printf("Element %d not found\n",data);

return start;

}

/*Deletion of first node*/

if(start->info==data)

{

tmp=start;

start=start->next;

start->prev=NULL;

free(tmp);

return start;

}

/*Deletion in between*/

tmp=start->next;

while(tmp->next!=NULL )

{

if(tmp->info==data)

{

tmp->prev->next=tmp->next;

tmp->next->prev=tmp->prev;

free(tmp);

return start;

}

tmp=tmp->next;

}

/*Deletion of last node*/

if(tmp->info==data)

{

tmp->prev->next=NULL;

free(tmp);

return start;

}

printf("Element %d not found\n",data);

return start;

}/*End of del()*/




struct node *reverse(struct node *start)

{

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;

}

start=p1;

printf("List reversed\n");

return start;

}