Я получаю неправильный вывод.

<pre>#include <iostream>
using namespace std;

class fraction
{
 long num;
 long den;

 public:
 fraction();
 fraction(long,long);
 fraction(const fraction &);
~fraction();

long getNum (void)const;
long getDen (void)const;
void print  (void);
fraction inc ();

friend fraction add (const fraction &f1, const fraction &f2);
friend fraction sub (const fraction &f1, const fraction &f2);
friend fraction mult(const fraction &f1, const fraction &f2);
friend fraction div (const fraction &f1, const fraction &f2);
};
fraction::fraction( )
{
  num = 0L ;
  den = 1L ;
}
fraction::fraction(long l_num,long l_den)
{
  num = l_num ;
  den = l_den ;
}
fraction::fraction(const fraction& f)
{
    num=f.num;
    den=f.den;
}
fraction:: ~fraction ( )
{
  //cout<<"Destructor"<<endl;
}
long fraction::getNum (void) const
{
  return num ;
}
long fraction::getDen (void) const
{
  return den ;
}
void fraction:: print (void)
{
    if(den==0)
       den=1L;
    cout<<num<<"/"<<den <<endl;
}
fraction fraction:: inc ( )
{
// long num ;
// long den ;
 long num = (num) + (den);
 long den = (den);
return fraction(num, den);
}
fraction add ( const fraction &f1,  const fraction &f2)
{
  long num = (f1.getNum ( ) * f2.getDen ( )) + ( f1.getDen ( ) * f2.getNum ( ) );
  long den = (f1.getDen ( ) * f2.getDen ( ));
  return fraction(num, den);
}
fraction sub ( const fraction &f1,  const fraction &f2)
{
  long num = (f1.getNum ( ) * f2.getDen ( )) - ( f1.getDen ( ) * f2.getNum ( ) );
  long den = (f1.getDen ( ) * f2.getDen ( ));
  return fraction(num, den);
}
fraction mult ( const fraction &f1,  const fraction &f2)
{
 long num = (f1.getNum ( ) * f2.getNum ( ));
 long den = (f1.getDen ( ) * f2.getDen ( ));
 return fraction(num, den);
}
fraction div  ( const fraction &f1,  const fraction &f2)
{
long num = (f1.getNum ( ) * f2.getDen ( ));
long den = (f1.getDen ( ) * f2.getNum ( ));
return fraction(num, den);
}

int main()
{
fraction f1,f2(5L,0L);
fraction f3(f2);
f1.print();
f2.print();
f3.print();

f3 = add(f3 , fraction (-7,8) );
f1 = add(f2,f3);
f1.print ();

f1 = sub(f2 , f3);
f1.print();

f1 = mult(f2, f3);
f1.print();

f1.inc().inc().print();
f1=div(f2 , f3 );
f1.print();

return 0;
}

I am getting wrong output on 7th output.I should get 181/8. but I am getting 7012088/165. I think it is due to uninitialized parameters, but still could not figure out. Please advice. Thank you