INHERITANCE dalam C++

#include <cstdlib>
#include <iostream>

using namespace std;
class Bilangan{
friend ostream&operator<<(ostream&,const Bilangan&);
friend istream&operator>>(istream&,Bilangan&);

public:
Bilangan(int a0=0,float b0=0.0):a(a0),b(b0){}
void banding_int(const Bilangan&,const Bilangan&);
Bilangan& operator=(const Bilangan&);
Bilangan operator+(const Bilangan&)const;
Bilangan operator-()const;

protected :
int a;
float b;
};

ostream& operator<<(ostream&out,const Bilangan & x)
{
out<<"Bagian integer:"<<x.a<<endl;
out<<"Bagian float:"<<x.b<<endl;
return out;
}

void Bilangan::banding_int(const Bilangan& x,const Bilangan& y)
{
if(x.a>y.a)cout<<x.a<<"::x lebih besar dari"<<y.a<<"::y";
else cout<<x.a<<"::x lebih kecil dari"<<y.a<<"::y";
}

Bilangan& Bilangan::operator=(const Bilangan& x)
{
a =x.a;
b =x.b;
return*this;
}

istream& operator>>(istream& in, Bilangan& x)
{
cout<<"\nMasukkan bagian integer:";
in>>x.a;
cout<<"Masukkan bagian float:";
in>>x.b;
return in;
}

Bilangan Bilangan::operator+(const Bilangan& x)const
{ Bilangan cc;
cc.a=a+x.a;
cc.b=b+x.b;
return cc;
}

Bilangan Bilangan::operator-()const
{ Bilangan x;
x.a= -a;
x.b= -b;
return x;
}

class Bil_char:public Bilangan{
  friend ostream& operator<<(ostream&,const Bil_char&);
public:
  Bil_char(int a0=0,int b0=0,char ch='x')
     :Bilangan(a0,b0),c(ch){}
private:
  char c;
};

ostream& operator <<(ostream& out,const Bil_char& x)
{
out<<"Bagian integer:"<<x.a<<endl;
out<<"Bagian float:"<<x.b<<endl;
out<<"Bagian char:"<<x.c<<endl;
return out;
}

int main(int argc, char *argv[])

{
   Bilangan s,t(-2,3.14),d;
   cout<<"Nilai awal s\n" << s;
   cout<<"Nilai awal t dari deklarasi\n"<<t;
   s=t;
   cout<<"Setelah s di-assign t\n";
   cout<<"Nilai s\n"<<s;
   cout<<"Masukkan nilai-nilai objek d";
   cin>>d;
   cout<<"Setelah d+t=.\n"<<d+t;;
   cout<<"Nilai d dinegatifkan\n"<< -d;
   Bil_char ss;
   cout<<"Nilai awal ss\n"<<ss;

    system("PAUSE");
    return EXIT_SUCCESS;
}