C++ :: Does Polymorphism Affects Operators Overloading?

I must overload [] but at the same time I must use polymorphism. I wonder if using polymorphism affects operators overloading since when I modified the first class by writing "virtual":

virtual void mostrarDatos(char*, char*, char*);
virtual void calcularEdad(int);

So I can do the polymorphism, it affects the part of the code where suppose to do an addition:

s=student1+=student2;
t=student3+=student4;
u=s+=t;

if I do that, it shows some strange numbers instead of the right ones. Here is the complete code:

.h
#ifndef PERSON_H
#define PERSON_H
#include <iostream>
using namespace std;
class persona {

[Code] ......