Access violation exeption in c++

Question

I'm trying to learn c++, I've read a lot about it and get it, but every time I program something that uses OOP concepts I have memory problems.

This is the exeption I'm getting with my code:

First-chance exception at 0x002EFB60 in Mathmatician.exe: 0xC0000005: Access violation executing location 0x002EFB60.

If there is a handler for this exception, the program may be safely continued.

So my question here is: what is wrong with my specific code? And more importantly, how can I avoid such exeptions? Are ther rules of thumb in c++ to avoid these?

And another thing: How can I avoid returning a local variable from a function that gets deleted (I assume just return the value itself, not a pointer?)

(More info:This specific code will be used to calculate derivative, with diffrent formulas like devision, multiplication, and more inhereting from the Form virtual class)

// Mathmatician.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <typeinfo>
#include <iostream>
using namespace std;


#include <sstream>

template <typename T>
  std::string NumberToString ( T Number )
  {
     std::ostringstream ss;
     ss << Number;
     return ss.str();

  }

class Form {
public:
    virtual Form& Derive() = 0;
    
    Form& operator+(Form& const other); 
    Form& operator*(Form& const other); 
    virtual string Print() = 0;
};

class Number : public Form {
public:
    int a;
    Number(int a) : a(a)
    {}

     Form& Derive() 
    {
        return (Form&) Number(0);
    }
    
    string Print() 
    {
        return NumberToString(a);
    }
};

class Addition : public Form {
private:
     Form& a;
     Form& b;
public:
    Addition(Form& const a, Form& const b) : a(a),b(b)
    {
    }
    Form& Derive()
    {
        return a.Derive() + b.Derive();
    }
    
    string Print() 
    {
        return "("+a.Print();// + "+" + b.Print()+")";
    };
};

class Multiply : public Form {
private:
     Form& a;
     Form& b;
public:
    Multiply(Form& a, Form& b) : a(a),b(b)
    {
    }
    Form& Derive()
    {
        return *new Addition(a.Derive(),b.Derive());
        //return a.Derive()*b + b.Derive()*a;
    }
    
    string Print() 
    {
        return "("+a.Print() + "*" + b.Print()+")";
    };

};

inline Form& Form::operator+(Form& const other) // copy assignment
{
    return Addition(*this,other);
    //LocationNode* A = new LocationNode('A',1,2);
}
inline Form& Form::operator*(Form& const other) // copy assignment
{
    return Multiply(*this,other);
}

int _tmain(int argc, _TCHAR* argv[])
{
    Form* n = &(*new Addition((Form&)*new Number(5),(Form&)*new Number(5))).Derive();
    cout << (*n).Derive().Print() << "/n";

    return 0;


}

Thank you!

Answer 1

You may see my answer here. The problem of new is that it does not clear the memory of the allocated space. The solution for new is to add the following line as long as you initialized the elements.

memset(element,0,sizeof(element));

Therefore you can ensure there is no garbage in the memory.

This answer is somehow based on my C language experience. Recently I found that C++ has another function called std::fill

using namespace std;
/* some function */
        fill(elem,elem+sizeof(elem),0);
/* end of some funtion */