Answer to Question #256118 in C for Jahnvi

Question

Explain queue with the help of an example(Example required).

Answer 1

A queue in C is a linear data structure to store and manipulate the data elements. It follows the order of First In First Out (FIFO).

In queues, the first element entered into the array is the first element to be removed from the array.

Example 

#include <stdio.h>
#include <stdlib.h>
struct Queue
{
	int *items;     
	int maxsize;    
	int front;      
	int rear;       
	int size;       
};
struct Queue* createNewQueue(int size)
{
	struct Queue *queue = NULL;
	queue = (struct Queue*)malloc(sizeof(struct Queue));
	queue->items = (int*)malloc(size * sizeof(int));
	queue->maxsize = size;
	queue->front = 0;
	queue->rear = -1;
	queue->size = 0;
	return queue;
}
int isEmpty(struct Queue *queue) {
	return queue->size==0;
}
int Peek(struct Queue *queue)
{
	if (isEmpty(queue))
	{
		printf("Queue is empty.\n");
	}else{
		return queue->items[queue->front];
	}
}
int isFull (struct Queue *queue) {
	return (queue->size == queue->maxsize);
}


void Enqueue(struct Queue *queue, int x)
{
	if (isFull(queue) == 1)
	{
		printf("Queue is full.\n");
	}else{
		queue->rear = (queue->rear + 1) % queue->maxsize;    
		queue->items[queue->rear] = x;
		queue->size++;
	}
}


void Dequeue(struct Queue *queue)
{
	if (isEmpty(queue))  
	{
		printf("Queue is empty.\n");
	}else{
		queue->front = (queue->front + 1) % queue->maxsize; 
		queue->size--;
	}
	
}
void Display (struct Queue *queue){
	int i;
	if (isEmpty(queue))  
	{
		printf("Queue is empty.\n");
	}else{
		printf("All values: \n");
		for(i = queue->front; i <= queue->rear; i++){
			printf("%d\n", queue->items[i]);
		}
	}
	
		
}


int main()
{
	struct Queue *queue = createNewQueue(5);


	Enqueue(queue, 1);
	Enqueue(queue, 2);
	Enqueue(queue, 3);
	Enqueue(queue, 4);


	Display(queue);


	Dequeue(queue);
	Dequeue(queue);
	Dequeue(queue);
	Dequeue(queue);


	Enqueue(queue, 5);
	Enqueue(queue, 6);


	if (isEmpty(queue)) {
		printf("The Queue is empty");
	}
	else {
		printf("The Queue is not empty");
	}


	getchar();
	getchar();
	return 0;
}