Communication between objects of different class c++ - c++

Question

How could I keep an object valid in a different class? Here is an example below.
This code would give as a result on the screen:
2
2
What I want is to give me this:
2
3
In other words, I desire object Bita (or even the whole class two) to acknowledge object Alpha and not create a new object.
Is there a way to include the object Alpha to object Bita ? Please be simple because I am a beginner.
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <stdlib.h>
#include <stdio.h>
using namespace std;
class one
{
int a, b;
public:
one() { a = 2; }
int func()
{
return a;
}
void func2()
{
a = 3;
}
};
class two
{
int z, b;
public:
void test();
};
void two::test()
{
one Alpha;
cout << Alpha.func() << '\n';
}
int main()
{
one Alpha;
cout << Alpha.func() << '\n';
Alpha.func2();
two Bita;
Bita.test();
return 0;
}

Answer 1

Each instance of an object has its own values for its member variables. So when you declare two Bita, and call Bita.test(), test() creates its own object of class Alpha inside of it, with its own value, which is still at 2, prints that, and then that Alpha object goes out of scope and is removed from the stack as test() completes.
What you say you have in mind to do here is to have class one have what is called a static member variable. Add the keyword static:
static int a;
And then a will behave as you intend.
One explanation of this is here: http://www.learncpp.com/cpp-tutorial/811-static-member-variables/

Answer 2

One solution would be to pass the object by reference you method two::test like this
class two
{
int z, b;
public:
void test(one& a);
};
void two::test(one& a)
{
cout << a.func() << '\n';
}
And then call it in main
Bita.test(Alpha);
So the full code will be
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <stdlib.h>
#include <stdio.h>
using namespace std;
class one {
int a, b;
public:
one() { a = 2; }
int func() { return a; }
void func2() { a = 3; }
};
class two {
int z, b;
public:
void test(one&);
};
void two::test(one& a) {
cout << a.func() << '\n';
}
int main() {
one Alpha;
cout << Alpha.func() << '\n';
Alpha.func2();
two Bita;
Bita.test(Alpha);
return 0;
}