Swapping by friend function in c++

#include<iostream>
using namespace std;
class alpha;
class beta
{
int a;
public :
void getvalue()
{
cin>>a;
}
void show()
{
cout<< a;
}
friend void swap (alpha &,beta&);
};
class alpha
{
int a;
public:
void getvalue()
{
cin>>a;
}
void show()
{
cout<< a;
}
friend void swap (alpha &,beta&);


};
void swap(alpha &x,beta &y)
{
int temp;
temp=x.a;
x.a=y.a;
y.a=temp;
}
int main()
{
alpha p;
beta q;
p.getvalue();
q.getvalue();
cout<<"Before swapping: ";
p.show();
cout<<" ";
q.show();
swap(p,q);
cout<<"\nAfter swapping: ";
p.show();
cout<<" ";
q.show();
}