queueusinglinklist.c

// A C program to demonstrate linked list based implementation of queue 
#include <stdio.h> 
#include <stdlib.h> 

// A linked list (LL) node to store a queue entry 
struct QNode { 
	int key; 
	struct QNode* next; 
}; 

// The queue, front stores the front node of LL and rear stores the 
// last node of LL 
struct Queue { 
	struct QNode *front, *rear; 
}; 

// A utility function to create a new linked list node. 
struct QNode* newNode(int k) 
{ 
	struct QNode* temp = (struct QNode*)malloc(sizeof(struct QNode)); 
	temp->key = k; 
	temp->next = NULL; 
	return temp; 
} 

// A utility function to create an empty queue 
struct Queue* createQueue() 
{ 
	struct Queue* q = (struct Queue*)malloc(sizeof(struct Queue)); 
	q->front = q->rear = NULL; 
	return q; 
} 

// The function to add a key k to q 
void enQueue(struct Queue* q, int k) 
{ 
	// Create a new LL node 
	struct QNode* temp = newNode(k); 

	// If queue is empty, then new node is front and rear both 
	if (q->rear == NULL) { 
		q->front = q->rear = temp;
		printf("%d ",k); 
		return; 
	} 

	// Add the new node at the end of queue and change rear 
	q->rear->next = temp; 
	q->rear = temp;
	printf("%d ",k); 
} 

// Function to remove a key from given queue q 
void deQueue(struct Queue* q) 
{ 
	// If queue is empty, return NULL. 
	if (q->front == NULL) 
		return; 

	// Store previous front and move front one node ahead 
	struct QNode* temp = q->front; 

	q->front = q->front->next; 

	// If front becomes NULL, then change rear also as NULL 
	if (q->front == NULL) 
		q->rear = NULL; 
	
	free(temp); 
} 

// Driver Program to test anove functions 
void main() 
{ 
	struct Queue* q = createQueue(); 
	enQueue(q, 10); 
	enQueue(q, 20); 
	enQueue(q, 30); 
	enQueue(q, 40); 
	enQueue(q, 50);
	printf("\nDeleted element : %d \n", q->front->key);
	deQueue(q);
	printf("Deleted element : %d \n", q->front->key);
	deQueue(q);
	printf("Deleted element : %d \n", q->front->key);
	deQueue(q);
	 
	printf("Queue Front : %d \n", q->front->key); 
	printf("Queue Rear : %d", q->rear->key);  
}