Program for Doubly Linked List Operations

#include <stdlib.h>
typedef struct dnode
{
int data;
struct dnode *next,*prev;
}DNODE;
 
DNODE *InsFront(DNODE *, int);
DNODE *InsBefore(DNODE *, int,int);
DNODE *DelNode(DNODE *, int);
void Display(DNODE *);
 
main()
{
DNODE *start=NULL;		 /* Main Program */
int opn,elem,info,n,i;
do
{
clrscr();
printf("\n ### Doubly Linked List Operations ### \n\n");
printf("\n Press 1-Creation with front Insertion");
printf("\n       2-Insert Before a Given Node");
printf("\n       3-Delete a Given Node");
printf("\n       4-Display");
printf("\n       5-Exit\n");
printf("\n       Your option ? ");
scanf("%d",&opn);
switch(opn)
{
case 1:
printf("\n\nHow Many Nodes ?");
scanf("%d",&n);
for(i=1;i<=n;i++)
{
printf("\nRead the Data for Node %d ?",i);
scanf("%d",&elem);
start=InsFront(start,elem);
}
printf("\nDoubly Linked list with %d nodes is ready toUse!!\n",n);
break;
case 3: printf(" Read the Info of the Node to be deleted ? ");
scanf("%d",&info);
start=DelNode(start,info);
break;
case 2: printf(" Read the Data for New node\n");
scanf("%d",&elem);
printf(" Read the Info of the Node(to the left of which new node tobe inserted ? ");
scanf("%d",&info);
start=InsBefore(start,elem,info);
break;
case 4: printf(" Doubly Linked List is \n");
Display(start); break;
case 5: printf("\n\n Terminating \n\n"); break;
default: printf("\n\nInvalid Option !!! Try Again !! \n\n");
break;
}
printf("\n\n\n\n  Press a Key to Continue . . . ");
getch();
}while(opn != 5);
}
 
DNODE *InsFront(DNODE *start, int elem)
{
DNODE *temp;
temp=(DNODE *)malloc(sizeof(DNODE));
if( temp == NULL)
{ printf(" Out of Memory !! Overflow !!!");
return(start);
}
else
{
temp->data=elem;
temp->prev=NULL;
temp->next=start;
start->prev=temp;
printf(" New Node has been inserted at Front Successfully !!");
return(temp);
}
}
 
DNODE *InsBefore(DNODE *start, int elem,int info)
{
DNODE *temp,*t;
temp=(DNODE *)malloc(sizeof(DNODE));
if( temp == NULL)
{ printf(" Out of Memory !! Overflow !!!");
return(start);
}
else
{
temp->data=elem;
temp->next=NULL;
temp->prev=NULL;
 
if(start->data == info)    /* Front Insertion */
{ temp->next=start;
start->prev=temp;
return(temp);
}
else
{
t=start;
while( t != NULL && t->data != info)
t=t->next;
if(t->data == info) /* Node found */
{
temp->next=t;
temp->prev=t->prev;
t->prev->next=temp;
t->prev=temp;
}
else
printf(" Node not found,Invalid Info !!!");
return(start);
}
}
}
 
DNODE *DelNode(DNODE *start, int info)
{
DNODE *t;
if( start ==  NULL) { printf(" Underflow!!!"); return(start); }
else
{ t=start;
if(start->data == info)    /* Front Deletion */
{ start=start->next;
start->prev=NULL;
t->next=NULL;
free(t);
return(start);
}
else
{
while( t != NULL && t->data != info)
t=t->next;
if(t->data == info) /* node to be deleted  found*/
{
t->prev->next=t->next;
t->next->prev=t->prev;
t->next=t->prev=NULL;
free(t);
}
else
printf("Node not found, Invalid Info !!");
return(start);
}
}
}
void Display(DNODE *start)
{ 
DNODE *t;
if( start == NULL) printf("Empty List\n");
else
{
t=start;
printf("Forward Traversal \n\n Start->");
while(t)
{
printf("[%d]->",t->data);
t=t->next;
}
printf("Null\n");
}
}