Insert New Node at begining of Linked List


In order to insert a new node at the beginning of the list we have to follows the below steps:
(1) First we have to check weather free node is available in the Availability Stack or not. If free node is available then we can allocate memory to new node.
(2) After creating new node we have to check weather linked list is empty or not. We have two possibilities:
(A) Linked List is empty (FIRST=NULL). In this case the newly created node becomes the first node of linked list.
(B) Linked List is not empty (FIRST ≠ NULL). In this case we can insert new node at the beginning of linked list. Now new node becomes the first node.

     

Algorithm to Insert New Node at begining of Linked List


Step 1: If AVAIL=NULL then
           Write “Availability Stack is Empty”
           Else
           NEW_NODE=AVAIL
           AVAIL = AVAIL->LINK
Step 2: If FIRST = NULL then
              NEW_NODE -> INFO = X
           NEW_NODE -> LINK = NULL
           FIRST = NEW_NODE
           Else
           NEW_NODE -> INFO = X
           NEW_NODE -> LINK = FIRST
           FIRST = NEW_NODE
Step 3: Exit


Program to Insert New Node at begining of Linked List


#include<stdio.h>
#include<conio.h>
#include<alloc.h>
struct node
{
      int info;
      struct node *link;
};
struct node *FIRST;
void createlist()
{
      char ch;
      printf("Enter n for break\n");
      ch=getchar();
      while(ch!='n')
      {
      struct node *NEW_NODE,*SAVE;int x;
  NEW_NODE=(struct node *)malloc(sizeof(struct   node));
      printf("Enter Data:");
      scanf("%d",&x);
      NEW_NODE->info=x;
      if(FIRST==NULL)
      {
         NEW_NODE->link=NULL;
         FIRST=NEW_NODE;
      }
      else
      {
         SAVE=FIRST;
         while(SAVE->link!=NULL)
         {
            SAVE=SAVE->link;
         }
         SAVE->link=NEW_NODE;
         NEW_NODE->link=NULL;
      }
      fflush(stdin);
      printf("Enter n for break\n");
      ch=getchar();
   }
}
void insertbeg()
{
      struct node *NEW_NODE;
      int x;
      NEW_NODE=(struct node *)malloc(sizeof(struct node));
      printf("Enter value of node:");
      scanf("%d",&x);
      NEW_NODE->info=x;
      if(FIRST==NULL)
      {
         NEW_NODE->link=NULL;
         FIRST=NEW_NODE;
      }
      else
      {
         NEW_NODE->link=FIRST;
         FIRST=NEW_NODE;
      }
      printf("%d is succesfully inserted\n",x);
      return;
}
void display()
{
      struct node *SAVE;
      if(FIRST==NULL)
      {
         printf("Linked List is empty\n");
         return;
      }
      printf("elements are:\n");
      SAVE=FIRST;
      while(SAVE!=NULL)
      {
         if(SAVE->link==NULL)
         printf("|%d|",SAVE->info);
         else
         printf("|%d|->",SAVE->info);
         SAVE=SAVE->link;
      }
      printf("\n");
      return;
}
void main()
{
      clrscr();
      FIRST=NULL;
      createlist();
      display();
      insertbeg();
      display();
      getch();
}

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