C Program to Perform Operations on The Doubly Linked List

				
					#include<stdio.h>

#include<stdlib.h>

struct node {
  int info;
  struct node * lptr, * rptr;
}* l, * r;
void doubins(int);
void doubdel(int);
void display();
int chk;
void main() {
  int ch, x;
  l = NULL;
  r = NULL;
  do {
    printf("\n Press:=>\n");
    printf("\n 1.Insert Node");
    printf("\n 2.Delete Node");
    printf("\n 3.Display Doubly Linked List");
    printf("\n 4.Exit");
    printf("\n Enter Choice: ");
    scanf("%d", & ch);
    switch (ch) {
    case 1:
      printf("\n\t Enter Element: ");
      scanf("%d", & x);
      doubins(x);
      display();
      break;
    case 2:
      printf("\n\t Enter Element which you want to Delete: ");
      scanf("%d", & x);
      chk = 0;
      if (l != NULL) //if(r!=NULL)
      {
        printf("\n\n Before Deletion:=>");
        printf("\n----------------");
        display();
      }
      doubdel(x);
      if (chk == 0) //if(r!=NULL)
      {
        printf("\n\n\n\n\n After Deletion:=>");
        printf("\n---------------");
        display();
      }
      break;
    case 3:
      display();
      break;
    case 4:
      exit(0);
    default:
      printf("\n\t Invalid Choice.\n\tTry Again.");
    }
  } while (ch != 4);
}
void doubins(int x) {
  struct node * New, * temp;
  New = (struct node * ) malloc(sizeof(struct node));
  New -> info = x;
  if (l == NULL) //if(r==NULL)
  {
    New -> lptr = NULL;
    New -> rptr = NULL;
    l = New;
    r = New;
    return;
  }
  if (x <= l -> info) //If the Node is less than all the Nodes
  {
    New -> lptr = NULL;
    New -> rptr = l;
    l -> lptr = New;
    l = New;
    return;
  }
  temp = l; //If the Node is inserted in between two nodes
  while (temp -> info < x && temp != NULL)
    temp = temp -> rptr;
  if (temp != NULL) {
    New -> lptr = temp -> lptr;
    New -> rptr = temp;
    temp -> lptr = New;
    New -> lptr -> rptr = New;
    return;
  }
  New -> rptr = NULL; //Node is inserted at last
  New -> lptr = r;
  r -> rptr = New;
  r = New;
}

void doubdel(int x) {
  struct node * temp;
  if (l == NULL) //if(r==NULL)
  {
    printf("\n\n\tDoubly Linked List Underflow on Delete.");
    chk = 1;
    return;
  }
  if (x == l -> info) //If First Node is tobe Deleted
  {
    temp = l;
    l = l -> rptr;
    l -> lptr = NULL;
    free(temp);
    return;
  }
  if (x == r -> info) //If Last Node is tobe Deleted
  {
    temp = r;
    r = r -> lptr;
    r -> rptr = NULL;
    free(temp);
    return;
  }
  temp = l;
  while (temp -> info != x && temp != NULL)
    temp = temp -> rptr;
  if (temp == NULL) //If Node not found in the List
  {
    /*    gotoxy(1,13);
        delline();
        gotoxy(1,13);
        delline();
        gotoxy(1,14);
        delline();
        gotoxy(1,16);
        delline();
        gotoxy(1,17);
        delline();
        gotoxy(1,18);
        delline();
        gotoxy(10,13);
        printf("\n\tNode not found.");
        chk=1;
        return; */
  }
  temp -> lptr -> rptr = temp -> rptr;
  temp -> rptr -> lptr = temp -> lptr;
  free(temp);
  return;
}

void display() {
  struct node * temp;
  if (l == NULL) //if(r==NULL)
    printf("\n\n\tDoubly Linked List is Empty.");
  else {
    printf("\n\nDoubly Linked List:\n\n\n");
    printf("l = %u\n\n", l);
    temp = l;
    while (temp != NULL) {
      printf("[%u|%u|%d|%u]->", temp, temp -> lptr, temp -> info, temp -> rptr);
      temp = temp -> rptr;
    }
    printf("NULL");
    printf("\n\nr = %u", r);
  }
}