Классы в C++. Переворот дроби.

#include <iostream>
using namespace std;
class rational
{
private:
int a;
int b;
public:
// default constructor
rational()
{
}
// constructor creating a fraction by parameters
rational(int a, int b = 1)
{
rational::a = a; rational::b = b;
}
// copy-constructor
rational(const rational& q)
{
a = q.a; b = q.b;
}
~rational()
{
}
rational add(const rational& v) const;
void afis();
};
rational rational::add(const rational& v) const
{
rational r;
r.a = a * v.b + b * v.a;
r.b = b * v.b;
return r;
}
void rational::afis()
{
cout << a << '/' << b;
}
int main( )
{
rational c(1,2), d(3,2), z;
c.afis(); cout << " + "; d.afis(); cout << " = "; 
z=c.add(d); z.afis(); cout << endl << endl;
rational C = c, D = rational(3,6);
C.afis(); cout << " + "; D.afis(); cout << " = "; 
z=C.add(D); z.afis(); cout << endl << endl;
rational F(C), M(4);
F.afis(); cout << " + "; M.afis(); cout << " = "; 
z=F.add(M); z.afis(); cout << endl << endl;
rational B(2,3), G(D), S;
B.afis(); cout << " + "; G.afis(); cout << " = ";
S=B.add(G); S.afis();
2cout << endl << endl;
rational *p, x; p=new rational;
x=rational(2,3);
*p=rational(S);
x.afis(); cout << " + "; p->afis(); cout << " = ";
z=x.add(*p); z.afis();
cout << endl << endl;
return 0;
}