C++ Operator Overload assignment operator = (equals)

#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;

class DArray/*w ww .  j a va2s  .com*/
{
  public:
    DArray(int nLengthOfArray = 0): nLength(nLengthOfArray), pArray(nullptr){
        cout << "Creating DArray of length = " << nLength << endl;
        if (nLength > 0){
            pArray = new int[nLength];
        }
    }
    DArray(DArray& da){
        cout << "Copying DArray of length = " << da.nLength << endl;
        copyDArray(da);
    }
    ~DArray(){
        deleteDArray();
    }

    DArray& operator=(const DArray& s)
    {
        cout << "Assigning source of length = " << s.nLength << " to target of length = " << this->nLength << endl;

        deleteDArray();
        copyDArray(s);
        return *this;
    }

    int& operator[](int index)
    {
        return pArray[index];
    }

    int size() { return nLength; }

    void display(ostream& out)
    {
        if (nLength > 0)
        {
            out << pArray[0];
            for(int i = 1; i < nLength; i++)
            {
                out << ", " << pArray[i];
            }
        }
    }

  protected:
    void copyDArray(const DArray& da);
    void deleteDArray();

    int nLength;
    int* pArray;
};

void DArray::copyDArray(const DArray& source)
{
    nLength = source.nLength;
    pArray = nullptr;
    if (nLength > 0)
    {
        pArray = new int[nLength];
        for(int i = 0; i < nLength; i++)
        {
            pArray[i] = source.pArray[i];
        }
    }
}

void DArray::deleteDArray(){
    nLength = 0;
    delete pArray;
    pArray = nullptr;
}

int main(int nNumberofArgs, char* pszArgs[])
{
    DArray da1(5);
    for (int i = 0; i < da1.size(); i++)
    {
        // uses user defined index operator to access
        // members of the array
        da1[i] = i;
    }
    cout << "da1="; da1.display(cout); cout << endl;

    DArray da2 = da1;
    da2[2] = 20;   // change a value in the copy
    cout << "da2="; da2.display(cout); cout << endl;

    da2 = da1;
    cout << "da2="; da2.display(cout); cout << endl;

    return 0;
}

#include <iostream>
using namespace std;
class alpha/*from w  w  w.  jav  a 2s  .  c  o  m*/
{
   private:
       int data;
   public:
   alpha()                      //no-arg constructor
   { }
   alpha(int d)                 //one-arg constructor
   { data = d; }
   void display()               //display data
   { cout << data; }
   alpha operator = (alpha& a)  //overloaded = operator
   {
      data = a.data;            //not done automatically
      cout << "\nAssignment operator invoked";
      return alpha(data);       //return copy of this alpha
   }
};
int main()
{
   alpha a1(37);
   alpha a2;
   a2 = a1;                        //invoke overloaded =
   cout << "\na2="; a2.display();  //display a2
   alpha a3 = a2;                  //does NOT invoke =
   cout << "\na3="; a3.display();  //display a3
   cout << endl;
   return 0;
}