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();
}

Thx everyone !
that was really helpful !

// C++ code by using class template!

#include<bits/stdc++.h>
using namespace std;

// One Limitation with array based queue is that max size of queueArr pehle se define karni padhegi and so result can overflow.
// To avoid this when overflow is done, tab ek new array bana do with twice the max size.

// We implement circular array for proper usage of memory allocated to us.
template
class Queue{
private:
T* queueArr;
int frontIndex;
int rearIndex;
int mxSize;
public:
// Constructor
Queue(int len);
// Destructor
~Queue();
// Member functions
void push(T val);
void pop();
T front();
void display();
bool empty();
};

template
Queue ::Queue(int len){
mxSize= len;
frontIndex=-1; rearIndex=-1;
queueArr= new T[mxSize];
}

template
Queue ::~Queue(){
delete[] queueArr;
}

template
void Queue::push(T val){
if(rearIndex+1==frontIndex) cout << "Overflow\n";
else{
if(frontIndex==-1 && rearIndex==-1){ frontIndex=0; rearIndex=0; }
else rearIndex=(rearIndex+1)%mxSize;
queueArr[rearIndex]=val;
}

}

template
void Queue::pop(){
if(frontIndex==-1 && rearIndex==-1) cout << "Queue is empty, nothing to pop.\n";
else if(frontIndex==rearIndex){ frontIndex=-1; rearIndex=-1; }
else frontIndex=(frontIndex+1)%mxSize;
}

template
T Queue::front(){
if(frontIndex==-1 && rearIndex==-1){ cout << "Queue is empty, nothing on top.\n"; return INT_MIN; }
else return queueArr[frontIndex];
}

template
void Queue::display(){
if(frontIndex==-1 && rearIndex==-1) cout << "Queue is empty, nothing to display.\n";
else{
int i=frontIndex;
while(i!=rearIndex){
cout << queueArr[i] << " ";
i=(i+1)%mxSize;
}
cout << queueArr[rearIndex] << "\n";
}
}

template
bool Queue::empty(){
if(frontIndex==-1 && rearIndex==-1) return true;
else return false;
}

int main(){
Queue q(10);
// for(int i=0;i<10;++i) q.push(i+1);
q.push(10);
q.display();
q.pop();
q.display();
q.push(11);
q.display();
q.pop();
if(q.front()!=INT_MIN) cout << q.front() << endl;
cout << q.empty() << endl;

return 0;

}

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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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