Queue with dynamically created array of user-defined type

[longberns]

I have built a queue class that handles some songs.
Program specs:
Queue has data members
- pointer to an array
- size of array
- index of first and last element in the array

Member functions
Enter data last in the queue
Delete item from the beginning

When a queue object is created, it should be able to handle 5 songs, if there is a need for more songs, let the size increase by 5.

This is my code

  // in songQ.h
#ifndef SONGQ_H
#define SONGQ_H

#include <iostream>
#include "song.h"
#define ARRAY_SIZE 5
using namespace std;
typedef Song Item;

class SongQ
{
private:
	Item *songArr;
	int front;   // index of queue's first element
	int back;    // index of queue's last element
	int size;
	int maxSize;

	// member functions
public:
	SongQ();
	
	~SongQ();
	void insertBack(Item &item);
	void deleteFront();
	bool isEmpty();
	bool isFull();
	int getSize() const;

	const SongQ &operator=(const SongQ &q);  // copy constructor
};

// in songQ.cpp
#include "songQ.h"

// Default constructor
SongQ::SongQ(): maxSize(5)
{
	front	= 0;
	back	= -1;
	size	= 0;
	songArr = new Item[maxSize];
}


// Destructor
SongQ::~SongQ()
{
	delete[] songArr;
	songArr = nullptr;
}

// insert an item at the back of the queue
void SongQ::insertBack(Item & item)
{
	songArr[++back] = item;

// THIS IS MY PROBLEM. When size is 5, program crasches. I need help here
	if (isFull())
	{
// create a new item, copy songArr to the item, delete songArr, point songArr to 
// the new item with the new size
		Item *tmpItem;
		tmpItem = new Item[size];

		for (int i = 0; i < size; i++)
		{
			songArr[i] = tmpItem[i];
		}
		delete[] songArr;

		maxSize += 5;

		tmpItem[maxSize] = *songArr;
	}

}

// Delete an item from the front
void SongQ::deleteFront()
{
	if (isEmpty())
	{
		cout << " Cannot delete from an empty queue!" << endl;
	}
	else
	{
		cout << songArr[front++] << endl; // i cout it because of specs
	}
}

// Check if queue is empty
bool SongQ::isEmpty()
{
	return (front > back);
}

// check that queue is full
bool SongQ::isFull()
{
	return back ==maxSize;
}

// get size of array
int SongQ::getSize() const
{
	return back - front + 1;
}

// copy constructor to copy one queue to the other
const SongQ & SongQ::operator=(const SongQ & q)
{
	if (this != &q)  // check that q is not the same as the other array
	{
		delete[]songArr;   // delete current array
		songArr = new Song[q.size];  // create space in the memory for the new array
		size = q.size;

		// copy elements for elements
		for (int i = 0; i < q.size; i++)
			songArr[i] = q.songArr[i];
	}
	return *this;
}

As commented, i need help with increase the array size to 5 when the size is five or when array becomes full.

Thanks in advance

[coder777]

Consider this:

		Item *tmpItem = songArr;

		maxSize += 5;

		songArr = new Item[maxSize];

		for (int i = 0; i < size; i++)
		{
			songArr[i] = tmpItem[i];
		}
		delete[] tmpItem;

[longberns]

Thanks @coder777. That fixes the problem.

But, i wonder why this function doen't get me the front value. It captures an empty space and prints it out

1 2 3 4 5 6 7 8 9 10 11 12 13

// Delete an item from the front void Queue::deleteFront() { if (isEmpty()) { cout << " Cannot delete from an empty queue!" << endl; } else { cout << songArr[front++] << endl; } }

// I get Front | |0 // instead of Jungele|B Gir|185 // songTitle(string), songArtist(string), songPlayTime(int)

In addition, the program runs successfully at first execution. When i try to re-run the program, it crashes and debugger sends me to check my isFull() function which is

// check that queue is full
bool Queue::isFull()
{
	return back == maxSize;
}

I have tried

 
bool Queue::isFull()
{
	return back % maxSize == 0;
} 
// At least with this, the program can be re-run many times but maxSize is 10 from start 

But after inserting 4 items in the queue, i get

 Size of q 4
 Max size of q now 10

And after adding 2 more items in the queue, size is now correctly reported as 6 but maxSize seems to have been 10 from the beginning

 Max size of q now 10
 Size of q 6

[coder777]

Please post the relevant code to reproduce the problem.

isFull() certainly is not the problem. Maybe the stack is corrupt.