``````// Implementation of a Queue
// Demonstration from lectures in April 2020
// Marc Chee (cs1511@cse.unsw.edu.au)

#include <stdlib.h>
#include <stdio.h>
#include "queue.h"

struct queueInternals {
struct queueNode *head;
struct queueNode *tail;
};

struct queueNode {
struct queueNode *next;
int data;
};

// Create a new empty queue.
// return the Queue (pointer to the queueInternals)
Queue queueCreate() {
struct queueInternals *newQueue = malloc(sizeof(struct queueInternals));
newQueue->head = NULL;
newQueue->tail = NULL;
return newQueue;
}

// Create and add an element to a queue
void queueAdd(Queue q, int item) {
struct queueNode *newNode = malloc(sizeof(struct queueNode));
newNode->data = item;
newNode->next = NULL;

if (q->tail == NULL) {
// there are no nodes in the queue
q->head = newNode;
} else {
// there are nodes in the queue
q->tail->next = newNode;
}
q->tail = newNode;
}

// Remove oldest node in the queue (the head)
// return the value stored in that node
int queueRemove(Queue q) {
if (q->head == NULL) {
// list was empty
printf("Attempted to remove from an empty queue.\n");
exit(1);
}

// keep track of the node for removal
int returnData = q->head->data;
struct queueNode *remNode = q->head;

// move the head pointer to the second node (or NULL)
q->head = q->head->next;

if (q->head == NULL) {
// we removed the final node in the queue, which means
// tail is now not pointing at a node.
q->tail = NULL;
}

free(remNode);

return returnData;
}

``````

Resource created Tuesday 14 April 2020, 08:37:49 PM.

file: queue.c

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