INSERTION IN DOUBLY LINKED LISTInsertion in doubly linked list

A program to insert node in a doubly linked list ?

The following below a code that shows how to perform various insertion operations on the linked list.

#include<stdio.h> #include<conio.h> #include<malloc.h> #include<process.h> struct node     { int num; struct node *next; struct node *prev; };                           /* declaring a global node of type struct */ typedef struct node NODE;   /* providing a type definition to the above created structure */ NODE *head=NULL; /* declaring some of the global variable that would be used throughout the program */ NODE *temp, *first, last; int info; void display(); void insert_at_end(); void insert_at_begin(); void insert_at_specifiedpos(); void main()            /* starting the main method() */ { int i; clrscr(); printf("\nprogram for insertion in a doubly linked list :\n"); do { printf("\nEnter your choice :\n"); printf("\n1.Insert element at the end of the linkedlist :"); printf("\n2.Insert element at the begin of the linkedlist :"); printf("\n3.Insert at any specified position in the linkedlist :"); printf("\n4.Exit\n"); fflush(stdin); scanf("\n%d",&i); switch(i) { case 1: insert_at_end(); display(); break; case 2: insert_at_begin(); display(); break; case 3: insert_at_specifiedpos(); display(); break; case 4: exit(0); } } while(i<=4); getch(); } void insert_at_end() { printf("\nEnter your element in the linked list :"); scanf("%d",&info); temp=(NODE *)malloc(sizeof(NODE));   /* allocating memory for the node to be inserted */ temp->num=info; temp->next=NULL; temp->prev=NULL; if(head==NULL)                      /* checking whether list is empty */ { head=temp; first=temp; last=temp; } else { first=head; while(first->next!=last) { first=first->next; } first->next=temp; temp->prev=first; temp->next=NULL; last=temp; } } void display() { first=head; printf("\nStatus of the doubly linked list is as follows :\n"); while(first->next!=NULL)                  /* traversing the linked list */ { printf("\n%d",first->num); first=first->next; } } void insert_at_begin() { printf("\nEnter the value which do you want to insert at begining\n"); scanf("\n%d"&info); temp=(NODE *)malloc(sizeof(NODE)); temp->num=info; temp->next=NULL; temp->prev=NULL; if(head=NULL) { head=temp; last=temp; } else { temp->next=head; head->prev=temp; temp->prev=NULL head=temp; } } void insert_at_specifiedpos() { NODE *second; int node_num,info; int i=1; printf("\nEnter the nodenumber after which you want to insert new node\n"); scanf("%d",&node_num); printf("\nEnter the value of new node\n"); scanf("\n%d",&info); temp=(NODE *)malloc(sizeof(NODE)); temp->num=info; temp->next=NULL; temp->prev=NULL; first=head; while(i<node_num) { second=first; first=first->next; } temp->next=first; temp->prev=second; first->prev=temp; second->next=temp; } }