Queue implementation using Array in C++ - c++

Question

I have implemented an integer type Queue using an array in C++ as:
This is not a circular queue so we don't have to bother for the empty space after filling it once and then deleting some values.
class IntQueue
{
private:
int *queueArray;
int queueSize;
int rear, front;
public:
IntQueue(int); // Constructor
~IntQueue(void);
void Enqueue(int);
int Dequeue(void);
bool isFull(void);
bool isEmpty(void);
void Display(void);
};
// Constructor
IntQueue::IntQueue(int size)
{
queueArray = new int[size];
queueSize = size;
rear = -1;
front = -1;
}
// Destructor
IntQueue::~IntQueue(void)
{
delete [] queueArray;
}
// Enqueue function
void IntQueue::Enqueue(int num)
{
if (isFull())
{
cout << "The Queue is full.\n";
}
else
{
rear++;
queueArray[rear] = num;
}
}
// Dequeue function
int IntQueue::Dequeue()
{
int num;
if (isEmpty())
{
cout << "The Queue is empty.\n";
}
else
{
front++;
num = queueArray[front];
}
return num;
}
//isFull function
bool IntQueue::isFull(void)
{
bool status;
if (rear == queueSize - 1)
status = true;
else
status = false;
return status;
}
//isEmpty function
bool IntQueue::isEmpty(void)
{
bool status;
if (front == rear)
status = true;
else
status = false;
return status;
}
// Display function
void IntQueue::Display()
{
if(isEmpty())
{
cout << "The Queue is empty.\n";
}
for(int i = front++; i <= rear; i++)
{
cout << "queueArray[" << i << "] = " << queueArray[i] << endl;
}
}
// Main function
int main()
{
int option, queueCapacity, value;
cout << endl << "Enter size of queue: ";
cin >> queueCapacity;
IntQueue *queue = new IntQueue(queueCapacity);
Menu:
cout << endl << "Queue implementation using Array" << endl;
cout << "--------------------------------" << endl;
cout << "1. Enqueue" << endl;
cout << "2. Dequeue" << endl;
cout << "3. Display Queue" << endl;
cout << "4. Display Menu" << endl;
cout << "5. Exit" << endl;
cout << "--------------------------------" << endl;
YourOption:
cout << endl << "Your option: ";
cin >> option;
switch(option)
{
case 1:
// Enqueue
cout << "Enter value to enqueue: ";
cin >> value;
queue->Enqueue(value);
goto YourOption;
case 2:
// Dequeue
int data;
data = queue->Dequeue();
cout << data << " is dequeued!";
goto YourOption;
case 3:
// Display
queue->Display();
goto YourOption;
case 4:
goto Menu;
case 5:
exit(0);
default:
cout << "Invalid option!" << endl;
break;
}
delete queue;
return 0;
}
The variable rear is initially -1. I have checked isFull() function as if rear is equal to the size of Queue, then the queue is full, not otherwise. However, to check queue emptiness, I compared if rear == front, then empty, not otherwise. But after executing it, by opting 2 from the menu, it displays some random value sometimes and the message i.e., "The Queue is empty".
What is the problem in this example?

Answer 1

void enqueue(int x)
{
//cout << "Enter the DAta " << endl;
//cin >> x;
if (front==(rear+1)%size)
{
cout << "Queue Is overflow::" << endl;
return;
}
else if (rear==-1&&front==-1)
{
//cout << "enter the To EnQueue :" << endl;
front = rear = 0;
queue[rear] = x;
}
else if (rear==0 && front==0)
{
rear = rear + 1 % size;
queue[rear] = x;
}
else
{
rear++;
queue[rear] = x;
}
}

Answer 2

Your queue is working properly but you have need to check some variable values like in the Enqueue(int num) function you have forgot to update the variable front=0
void IntQueue::Enqueue(int num)
{
if (isFull())
{
cout << "The Queue is full.\n";
}
else
{
rear++;
queueArray[rear] = num;
}
}
because at the initial time when you display the values front=-1.
So, add the front=0 in the enqueue function like this,
void IntQueue::Enqueue(int num)
{
if (isFull())
{
cout << "The Queue is full.\n";
}
else
{
front=0;
rear++;
queueArray[rear] = num;
}
}
Hope you got it. if you have any confusion comment it.