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");
 }
}