Contoh Codingan Faktorial, Fibonanci & Biner Calculating C++

#include<iostream>

using namespace std;

class Bilangan
{
private:
long angka;
long hasil;
public:
//Bilangan(int hasil){hasil = 0;}

void setAngka(long angka)
{
this->angka = angka;
}

friend long getAngka(Bilangan &obj)
{
return obj.angka;
}

long getHasil() const{return hasil;}

void biner(int angka )
{
if(angka == 0)cout << "0 ";
else
{
biner(angka/2);
cout << angka%2 << " ";
}
}

int fibonacci(long angka);

~Bilangan(){}
};

int Bilangan::fibonacci(long angka)
{
if(angka == 0 || angka == 1)return angka;
else return fibonacci(angka - 1) + fibonacci(angka - 2);
}

inline long long int faktorial(Bilangan &obj)
{
long long temp=1;
for(int i = 1;i <= getAngka(obj);i++)
{
//cout << temp << endl;
temp *= i;
}

return temp;
}



void clear()
{
for(int i=0;i<25;i++)cout<<endl;
}

void menu()
{
cout << "Factorial, Fibonacci, and Biner Calculation" << endl
<< "===========================================" << endl << endl ;

cout << "1. Factorial" << endl;
cout << "2. Fibonacci" << endl;
cout << "3. Binary Number" << endl;
cout << "4. Exit" << endl;
}

void main()
{
Bilangan obj;
//cont object , atribut dr object tidak dapat dirubah
const Bilangan b;

int opt;
long long angka;

do
{
opt = 0;

clear();
menu();

do
{
cout << "Choose: ";
cin >> opt;cin.clear();cin.sync();
}while(opt < 1 || opt >4);

switch(opt)
{
case 1:
clear();
do
{
cout << "Input the number[1-20]: ";
cin >> angka;cin.clear();cin.sync();
}while(angka < 1|| angka > 20);

obj.setAngka(angka);


cout << endl << "The Result of Factorial " << getAngka(obj) << " : " << endl;
cout << faktorial(obj) << " ";
cin.get();
break;
case 2:
clear();
do
{
cout << "Input the number[1-20]: ";
cin >> angka;cin.clear();cin.sync();
}while(angka < 1|| angka > 20);

obj.setAngka(angka);


cout << endl << "The Result of Fibonacci " << getAngka(obj) << " : " << endl;
for(int i = 0;i< getAngka(obj);i++)
cout << obj.fibonacci(i) << " ";
cin.get();
break;
case 3:
clear();
do
{
cout << "Input the number[1-100]: ";
cin >> angka;cin.clear();cin.sync();
}while(angka < 1|| angka > 100);

obj.setAngka(angka);

cout << endl << "The Result of Binary Number " << getAngka(obj) << " : " << endl;
obj.biner(getAngka(obj));
cin.get();
break;
case 4:
clear();
cout << endl << endl << " Thank you and have a nice day.. ^^" << endl;
break;
}

}while(opt != 4);

cin.get();
}