Help with copy constructor

I am new to c++ programming.
I want to create a program which includes the following line of codes

Code:

class cars
{
.
.
.
};
class PatrolCars:public cars
{
.
.
.
};
class CNGCars:public cars
{
.
.
.
};

now what the problem is that i want to write a member function which can copy each of the drive class objects to each other I mean these lines should be valid

Code:

PatrolCars patcar;
CNGCars cngcar;
patcar=cngcar;

should i create a copy constructor or should i overload an operator for this?
plz help!

If they need to be assignable to each other why are they different types? It sounds like only SOME aspects of the objects should be copied. In that case, neither a copy constructor nor an assignment operator should be used, rather something more explicit like CopyCarAspects() or something. Otherwise you have code that does things which look like assignments but are not actually assignments.

An explicit function like copycarasspects() or something else will require an access to the member data of both types of objects. I dont want to do that.

It would actually require access to both types' members no matter what method you chose. You could write it in terms of public accessor functions.

you mean some thing like this could help

Code:

class cars
{
.
.
.
};
class PatrolCars:public cars
{
public:
void PatrolCar (CNGCars c1)
{
.
.
}
};
class CNGCars:public cars
{
.
public:
void CNGCars(PatrolCars pc1)
{
.
.
}
};