C++ Class

include <iostream>
using namespace std;
class PFArrayD
{
    public:
        PFArrayD();
        PFArrayD(int capacityValue);
        PFArrayD(const PFArrayD& pfaObject);
        void addElement(double element);
        bool full() const { return (capacity == used); }
        int getCapacity() const { return capacity; }
        int getNumberUsed() const { return used; }
        void emptyArray() { used = 0; }
        double& operator[](int index);
        PFArrayD& operator =(const PFArrayD& rightSide);
        ~PFArrayD();
    private:
        double *a;
        int capacity;
        int used;
};
PFArrayD::PFArrayD() :capacity(50), used(0){
    a = new double[capacity];
}
PFArrayD::PFArrayD(int size) : capacity(size), used(0){
    a = new double[capacity];
}
PFArrayD::PFArrayD(const PFArrayD& pfaObject): capacity(pfaObject.getCapacity()), used(pfaObject.getNumberUsed()){
    a = new double[capacity];
    for (int i = 0; i < used; i++)
    a[i] = pfaObject.a[i];
}
void PFArrayD::addElement(double element)
{
    if (used >= capacity){
        cout << "Attempt to exceed capacity in PFArrayD.\n";
        exit(0);
    }
    a[used] = element;
    used++;
}
double& PFArrayD::operator[](int index){
    if (index >= used){
        cout << "Illegal index in PFArrayD.\n";
        exit(0);
    }
    return a[index];
}
PFArrayD& PFArrayD::operator =(const PFArrayD& rightSide){
    if (capacity != rightSide.capacity){
        delete[] a;
        a = new double[rightSide.capacity];
    }
    capacity = rightSide.capacity;
    used = rightSide.used;
    for (int i = 0; i < used; i++)
    a[i] = rightSide.a[i];
    return *this;
}
PFArrayD::~PFArrayD(){
    delete[] a;
}
void testPFArrayD(){
    int cap;
    cout << "Enter capacity of this super array: ";
    cin >> cap;
    PFArrayD temp (cap);
    cout << "Enter up to " << cap << " nonnegative numbers. \n";
    cout << "Place a negative number at the end. \n";
    double next;
    cin >> next;
    while ((next >= 0) && (!temp.full())) {
        temp.addElement(next);
        cin >> next;
    }
    cout << "You entered the following " << temp.getNumberUsed() << " numbers:\n";
    int index;
    int count = temp.getNumberUsed();
    for (index = 0; index < count; index++)
        cout << temp[index] << " ";
    cout << endl;
    cout << "(plus a sentinel value.)\n";
}
​
int main() {
    cout << "This program tests the class PFArrayD.\n";
    char ans;
    do {
        testPFArrayD();
        cout << "Test again? (y/n) ";
        cin >> ans;
    } while ((ans == 'y') || (ans == 'Y'));
    //system("pause");
    return 0;