# Circular Queue Implementation in C++

In linear queue, when we delete any element, only front increment by one but position is not used later. So, when we perform more add and delete operations, memory wastage increases. But in circular queue, memory is utilized if we delete any element that position is used later due to its circular representation.

Algorithm for Circular Queue
1. Declare and initialize necessary variables such as head = 0, tail = 0 etc.
2. For enqueue operation,
If head = (tail+1)%MAXSIZE
print “Queue is Full”
Else
queue[tail] = item
tail = (tail+1)%MAXSIZE
3. For enqueue of next data item, goto step 2
4. For dequeue operation,
If head = tail
print “Queue is Empty”
Else
Remove item i.e. item = queue[head]
5. For next dequeue operation , goto step 4
6. Stop

Source Code for Circular Queue

#include<iostream>
#include<cstdlib>
#define MAX_SIZE 4

using namespace std;

class Queue{
private:
int item[MAX_SIZE];
int tail;
public:
Queue();
void enqueue(int);
int dequeue();
int size();
void display();
bool isEmpty();
bool isFull();
};

Queue::Queue(){
tail = 0;
}

void Queue::enqueue(int data){
item[tail] = data;
tail = (tail+1)%MAX_SIZE;
}

int Queue::dequeue(){
int temp;
return temp;
}

int Queue::size(){
return (tail - head);
}

void Queue::display(){
int i;
if(!this->isEmpty()){
cout<<item[i]<<endl;
}
}else{
cout<<"Queue Underflow"<<endl;
}
}

bool Queue::isEmpty(){
return true;
}else{
return false;
}
}

bool Queue::isFull(){
return true;
}else{
return false;
}
}

int main(){
Queue queue;
int choice, data;
while(1){
cout<<"\n1. Enqueue\n2. Dequeue\n3. Size\n4. Display all element\n5. Quit";
cout<<"\nEnter your choice: ";
cin>>choice;
switch(choice){
case 1:
if(!queue.isFull()){
cout<<"\nEnter data: ";
cin>>data;
queue.enqueue(data);
}else{
cout<<"Queue is Full"<<endl;
}
break;
case 2:
if(!queue.isEmpty()){
cout<<"The data dequeued is :"<<queue.dequeue();
}else{
cout<<"Queue is Emtpy"<<endl;
}
break;
case 3:
cout<<"Size of Queue is "<<queue.size();
break;
case 4:
queue.display();
break;
case 5:
exit(0);
break;
}
}
return 0;
}
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### 5 Responses

1. Anonymous says:

The code is wrong…. If the max_size is 4, it works only for 3 values… t

2. In circular queue there is always 1 blank space. So it works only for 3.

3. Anonymous says:

How does that size method work?

4. Cory says:

goodness, circular queues are so stupid. Linked lists make so much more sense.

5. Anonymous says:

The abs(head == tail) line is suspect