Question about static members

[cwj7897]

Hi everyone! I'm currently trying to learn C++. I wrote a small program to get a little practice and now I have a question about static data members. Here is my code:

#include <iostream>
using namespace std;

class myClass //define myClass
{
    private:
       int x;
       int y;
       static int used;//how many of the myClass objects is there
    public:
       myClass(); //general constructor
       myClass(int,int);//constructor taking values
      ~myClass(); //clean up
      void setX(int);//returns the x value
      void setY(int);//returns the y value
      int getX(); //return x value
      int getY(); //return y value
      int getSum(); //return x + y
      int getUsed(); //retrieves how many times has the class been used
      myClass operator +(myClass); //overloading the + operator
};

int myClass::used = 0; //initialize used to 0

myClass::myClass()
{
    //init data members to 0 and increse used by 1
    x = 0;
    y = 0;
    used++;
}

myClass::myClass(int a, int b)
{
    // init data members to values given and increse used by 1;
    x = a;
    y = b;
    used++;
}

myClass::~myClass()
{
    //clean up x & y and decrese used by 1
    delete &x;
    delete &y;
    used--;
}

void myClass::setX(int a)
{
    x = a;
}

void myClass::setY(int a)
{
    y = a;
}

int myClass::getX()
{
    return x;
}

int myClass::getY()
{
    return y;
}

int myClass::getSum()
{
    return x + y;
}

int myClass::getUsed()
{
    return used;
}

myClass myClass::operator+(myClass param)
{
   //allows the myClass object to be added with another myClass object
   myClass temp;
   temp.x = x + param.x;
   temp.y = y + param.y;
   return (temp);
}


int main()
{
    myClass mClassA;
    myClass mClassB(3,4);
    myClass mClassC;

    mClassA.setX(5);
    mClassA.setY(6);

    mClassC = mClassA + mClassB;

    cout << "mClassA.x = " << mClassA.getX()
         << "\nmClassA.y = " << mClassA.getY()
         << "\nmClassA.sum = " << mClassA.getSum() << endl
         << mClassA.getUsed() << endl
         << "\n\nmClassB.x = " << mClassB.getX()
         << "\nmClassB.y = " << mClassB.getY()
         << "\nmClassB.sum = " << mClassB.getSum() << endl
         << mClassB.getUsed() << endl
         << "\n\nmClassC.x = " << mClassC.getX()
         << "\nmClassC.y = " << mClassC.getY()
         << "\nmClassC.sum = " << mClassC.getSum() << endl
         << mClassC.getUsed() << endl
         << "\n\n\nTotal # of myClass used = " << mClassC.getUsed()
         << endl;

    cin.get();
    cin.get();

    return 0;
}

When I run the progam this is what I get:

mClassA.x = 5
mClassA.y = 6
mClassA.sum = 11


mClassB.x = 3
mClassB.y = 4
mClassB.sum = 7


mClassC.x = 8
mClassC.y = 10
mClassC.sum = 18



Total # of myClass used = 2

My question is this. If I created 3 myClass objects why is it returning that only 2 were created? Not expecting someone to give me the answer but a nudge in the right direction would be appreciated. Also any other tips or advice are welcome. Thanks in advance!

[helios]

There's one kind of constructor you're forgetting to implement.

By the way, lines 44 and 45 are problematic.

[guestgulkan]

Your result is misleading:
You have neglected to take into account the copy constructor (which is used in the operator+ function) - so the used variable does not get incremented when the copy is made - BUT the destructor decrements the used count when the copy is destroyed.

The Total # of myClass used value that you print out is also misleading - it is really a
printout of the number of myClass objects still in existance at that point (which would have said
3 if you had accounted for the copy constructor) - but really 5 had been created and 2 already destroyed.



PS:
This is wrong

myClass::~myClass()
{
    //clean up x & y and decrese used by 1
    delete &x;  //not correct
    delete &y; //not correct
    used--;
}

x and y were never allocated using the new operator.

[cwj7897]

Thanks helios, I'll go over constructors and deconstructors again. I thought that lines 44 and 45 might be a problem. I tried delete x; and delete y; but it gave me the error

 type 'int' argument given to 'delete', expected pointer 

. Looking back and thinking about it I can see where I went wrong. I didn't declare them as pointers so I shouldn't of used delete. Should I even worry about cleaning up x and y? I think I should just not sure how to go about it. Gives me something to think about. Any more nudges are appreciated. Thanks again.

[cwj7897]

Thanks for the insight guestgulkan. I honestly didn't even think of that. I appreciate it. I'm glad I found this site. I've learned a lot just going through the forums. Keep the nudges coming. :-)