Adding to dynamic array - c++

Question

Disclaimer: Yes, I know about std::vector. I'm doing this for the sake of learning.
I'm working on making a dynamic array class, and I'm trying to get add to work.
template <class T>
void Array<T>::add(T value)
{
T * tmp = new T[mCount];
for (int i = 0; i < mCount; i++)
{
tmp[i] = mData[i];
}
mCount++;
delete[] mData;
mData = tmp;
mData[mCount - 1] = value;
}
It works... sort of. The function works in adding the element, but then the program crashes when exiting. No errors, no nothing. It just freezes, and I have to close it using (Shift + F5).
So, what's wrong with this?
Here's my whole class. If I didn't include a function it means there's no code in it.
#ifndef ARRAY_H
#define ARRAY_H
using namespace std;
template <class T>
class Array
{
private:
T * mData;
int mCount;
public:
Array();
~Array();
void add(T value);
void insert(T value, int index);
bool isEmpty();
void display();
bool remove(T value);
bool removeAt(int index);
int size();
T & operator[](const int index);
};
// Constructors / Destructors
// --------------------------------------------------------
template <class T>
Array<T>::Array()
{
mCount = 0;
mData = new T[mCount];
for (int i = 0; i < mCount; i++)
mData[i] = 0;
}
template <class T>
Array<T>::~Array()
{
delete[] mData;
}
// General Operations
// --------------------------------------------------------
template <class T>
void Array<T>::add(T value)
{
T * tmp = new T[mCount];
for (int i = 0; i < mCount; i++)
{
tmp[i] = mData[i];
}
mCount++;
delete[] mData;
mData = tmp;
mData[mCount - 1] = value;
}
template <class T>
void Array<T>::display()
{
if (isEmpty())
{
cout
<< "The array is empty."
<< "\n\n";
return;
}
cout << "(";
for (int i = 0; i < mCount; i++)
{
cout << mData[i];
if (i < mCount - 1)
cout << ", ";
}
cout << ")" << "\n\n";
}
template <class T>
bool Array<T>::isEmpty()
{
return mCount == 0;
}
template <class T>
int Array<T>::size()
{
return mCount;
}
// Operator Overloads
// --------------------------------------------------------
template <class T>
T & Array<T>::operator[](const int index)
{
return mData[index];
}
#endif
If you need any additional info lemme know and I can post it.

Answer 1

Assuming mCount keeps the number of elements in the array, then when adding a new element you really have to allocate at least mCount + 1 elements (assuming of course you want to keep all the old ones and the new one) via:
T * tmp = new T[mCount + 1];
as opposed to:
T * tmp = new T[mCount];
If it's for anything else other than educational purposes, please use std::vector instead. For example your add function is not exception safe.