Queue - Array Implementation

Queue_CircularArrayImplementation.cpp

/* Queue - Circular Array implementation in C++*/
#include<iostream>
using namespace std; 
#define MAX_SIZE 101  //maximum size of the array that will store Queue. 

// Creating a class named Queue.
class Queue
{
private:
	int A[MAX_SIZE];
	int front, rear; 
public:
	// Constructor - set front and rear as -1. 
	// We are assuming that for an empty Queue, both front and rear will be -1.
	Queue()
	{
		front = -1; 
		rear = -1;
	}

	// To check wheter Queue is empty or not
	bool IsEmpty()
	{
		return (front == -1 && rear == -1); 
	}

	// To check whether Queue is full or not
	bool IsFull()
	{
		return (rear+1)%MAX_SIZE == front ? true : false;
	}

	// Inserts an element in queue at rear end
	void Enqueue(int x)
	{
		cout<<"Enqueuing "<<x<<" \n";
		if(IsFull())
		{
			cout<<"Error: Queue is Full\n";
			return;
		}
		if (IsEmpty())
		{ 
			front = rear = 0; 
		}
		else
		{
		    rear = (rear+1)%MAX_SIZE;
		}
		A[rear] = x;
	}

	// Removes an element in Queue from front end. 
	void Dequeue()
	{
		cout<<"Dequeuing \n";
		if(IsEmpty())
		{
			cout<<"Error: Queue is Empty\n";
			return;
		}
		else if(front == rear ) 
		{
			rear = front = -1;
		}
		else
		{
			front = (front+1)%MAX_SIZE;
		}
	}
	// Returns element at front of queue. 
	int Front()
	{
		if(front == -1)
		{
			cout<<"Error: cannot return front from empty queue\n";
			return -1; 
		}
		return A[front];
	}
	/* 
	   Printing the elements in queue from front to rear. 
	   This function is only to test the code. 
	   This is not a standard function for Queue implementation. 
	*/
	void Print()
	{
		// Finding number of elements in queue  
		int count = (rear+MAX_SIZE-front)%MAX_SIZE + 1;
		cout<<"Queue       : ";
		for(int i = 0; i <count; i++)
		{
			int index = (front+i) % MAX_SIZE; // Index of element while travesing circularly from front
			cout<<A[index]<<" ";
		}
		cout<<"\n\n";
	}
};
int main()
{
	/*Driver Code to test the implementation
	  Printing the elements in Queue after each Enqueue or Dequeue 
	*/
   Queue Q; // creating an instance of Queue. 
   Q.Enqueue(2);  Q.Print();  
   Q.Enqueue(4);  Q.Print();  
   Q.Enqueue(6);  Q.Print();
   Q.Dequeue();	  Q.Print();
   Q.Enqueue(8);  Q.Print();
}

For a C program
#include <assert.h> // assert
#include <stdlib.h> // malloc, free
#include <stdbool.h>
#include <stdio.h>

typedef struct node
{
int data;
struct node *next;
} node_t;

typedef struct
{
node_t *rear;
int size;
} queue_t;

queue_t *alloc_queue(void)
{
queue_t *queue = malloc(sizeof(queue_t));
assert(queue != NULL);

queue->rear = NULL;
queue->size = 0;
return queue;

}

void enqueue(queue_t queue, int value)
{
assert(queue!=NULL);
node_t newnode;
node_t *front;
newnode = malloc(sizeof(node_t));
assert(newnode!=NULL);
newnode->data = value;
newnode->next = NULL;
if(queue->rear==NULL) // if the queue is empty
{
queue->rear = newnode;
queue->rear->next = queue->rear;
}
else
{
front = queue->rear->next;
queue->rear->next = newnode;
queue->rear = newnode;
queue->rear->next = front;
}
queue->size++;
}

_

int main()
{
queue_t *queue = alloc_queue();
enqueue(queue, 40);
enqueue(queue, 30);
enqueue(queue, 20);
int a;
front(queue, &a);
}

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