Array Implementation of Queue: Strange Output - c++

Question

I am learning about queues and I wrote the following program which implements the queue as a linear array (NOT a circular one).
#include<iostream>
using namespace std;
class queue {
int front, max_queue, rear, count = 0;
int *items;
public:
queue(int);
~queue();
void enqueue(int);
void dequeue();
bool isEmpty();
int size();
void display();
};
queue::~queue() {
delete []items;
}
queue::queue(int max) {
front = -1;
rear = -1;
max_queue = max;
items = new int[max_queue];
}
void queue::enqueue(int n) {
if (count == max_queue)
cout << "queue is full, no enqueue possible";
else {
items[++rear] = n;
count++;
}
}
void queue::dequeue() {
if (count == 0)
cout << "no dequeue possible, queue already empty";
else {
front--;
count--;
}
}
bool queue::isEmpty() {
return ((count == 0) ? 1 : 0);
}
int queue::size() {
return count;
}
void queue::display() {
if (count == 0)
cout << "nothing to display";
else {
for (int i = front; i <= rear;)
cout << items[i++] << endl;
}
}
int main() {
queue *qe = new queue(10);
qe->enqueue(1);
qe->enqueue(2);
qe->enqueue(3);
qe->enqueue(4);
qe->display();
return 0;
}
I get the following output
49
1
2
3
4
RUN FINISHED; exit value 0; real time: 10ms; user: 0ms; system: 0ms
Why is there a 49 in my output.? Is it a garbage value? Does not using a circular array implementation,a probable cause?
I have no idea. Any help appreciated.

Answer 1

You're starting the display loop i with front which is -1. You're pointing to a spot before your queue.

Answer 2

If a queue is empty and you enqueue an element x, then x becomes both the front and the rear.

Answer 3

The issue is in your display function:
for (int i = front; i <= rear;)
cout << items[i++] << endl;
You're setting i=front, but you've previously set front=-1. Thus, you're attempting to access items[-1]. You can either set i=front+1:
for (int i = front + 1; i <= rear;)
cout << items[i++] << endl;
or continue until i<rear and use ++i instead of i++:
for (int i = front; i < rear;)
cout << items[++i] << endl;