Oct 11, 2011

C Program to implement QUEUE operations using Linked Lists

Data structures using C,
C Program to implement QUEUE operations using Linked list. Queue is a abstract data type, In which entities are inserted into the rear end and deleted from the front end. Here to implement queue we used the Linked lists!. Read more about C Programming Language .

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#include <stdlib.h>
typedef struct node {
 int data;
 struct node *link;

void Insert(int);
int Delete();
void Display();
NODE *front, *rear; /* Global Declarations */

main() {
 /* Main Program */
 int opn, elem;
 front = rear = NULL;
 do {
  printf("\n ### Linked List Implementation of QUEUE Operations ### \n\n");
  printf("\n Press 1-Insert, 2-Delete, 3-Display,4-Exit\n");
  printf("\n Your option ? ");
  scanf("%d", &opn);
  switch (opn) {
  case 1:
   printf("\n\nRead the Element to be Inserted ?");
   scanf("%d", &elem);
  case 2:
   elem = Delete();
   if (elem != -1)
    printf(" Deleted Node(From Front)with the Data: %d\n", elem);
  case 3:
   printf("Linked List Implementation of Queue: Status:\n");
  case 4:
   printf("\n\n Terminating \n\n");
   printf("\n\nInvalid Option !!! Try Again !! \n\n");
  printf("\n\n\n\n  Press a Key to Continue . . . ");
 } while (opn != 4);

void Insert(int info) {
 NODE *temp;
 temp = (NODE *) malloc(sizeof(NODE));
 if (temp == NULL)
  printf(" Out of Memory !! Overflow !!!");
 else {
  temp->data = info;
  temp->link = NULL;
  if (front == NULL) {
   front = rear = temp;
  } /* First Node? */
  else {
   rear->link = temp;
   rear = temp;
  } /* Insert End */
  printf(" Node has been inserted at End Successfully !!");

int Delete() {
 int info;
 NODE *t;
 if (front == NULL) {
  printf(" Underflow!!!");
  return -1;
 } else {
  t = front;
  info = front->data;
  if (front == rear)
   rear = NULL;
  front = front->link;
  t->link = NULL;
  return (info);

void Display() {
 NODE *t;
 if (front == NULL)
  printf("Empty Queue\n");
 else {
  t = front;
  while (t) {
   printf("[%d]->", t->data);
   t = t->link;
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