Rational Number using class

[Adasuna]

I complete this program, but the only thing is that it won't execute the program. Any idea what I did wrong????

edit- i found the problem, the other problem is the program is not running as it is suppose to.

#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <cctype>

using namespace std;

class Rational
{
	private:
		int numerator;
		int denominator;		
		int GCD(int, int); //Determine the GCD

	public:
		Rational();
		Rational(int, int);
		Rational(int);

		int getNumerator();
		int getDenominator();

		Rational add(Rational);
		Rational sub(Rational);
		Rational mul(Rational);
		Rational div(Rational);

		void reduction();
		void Numerator(int);
		void Denominator(int);
		void printans(); 
		void printnum();

};
bool valid(int den )// check if valid
{
  return (den > 0 || den < 0);
}
int main()
{
	cout << fixed << showpoint << setprecision(2);  //2 significant figures
	char again = 'y'; //Loop
	
	cout << "This program perfroms several arithmetic operations on two rational numbers." << endl << endl;
	
	while (toupper(again) == 'Y') //run again
	{
		int num, den;
		cout << "Enter a rational number (a/b): ";
		string f1;
		getline( cin, f1 );// get the entire string from the input
		cout << endl;

		 istringstream ss( f1 );
			char slash; //slash
			ss >> num >> slash >> den;

		return ss.eof() && (slash == '/') && valid(den);//Check string
		while (!(den) == 0) 
		{
			cout << "Error: Re-Enter the rational number (a/b): ";
			fflush(stdin);
			cin.clear();
		}
		Rational x = Rational(num, den);
		cout << "Just checking, make sure the number is simplified." << endl << endl;
		x.reduction(); //reduce user input
		
		cout << "Enter a rational number (a/b): ";
		string f2;
		getline( cin, f2 );// get the entire string from the input
		cout << endl;

		istringstream ss1( f2 );
		char divisor; //slash
		ss1 >> num >> divisor >> den;

		return ss.eof() && (divisor == '/') && valid(den);//Check string

		while (!(den) == 0) 
		{
			cout << "Error: Re-Enter the rational number (a/b): ";
			fflush(stdin);
			cin.clear();
		}
		Rational z = Rational(num, den);
		cout << "Just checking, make sure the number is simpfied." << endl << endl;
		x.reduction(); //reduce user input

		Rational rat;

		cout << endl << "Results of arithmetic operations:" << endl << endl;
		x.printans();
		cout << " + ";
		z.printans();
		cout << " = ";
		rat = x.add(z);
		rat.printans();
		cout << " = ";
		rat.printnum();
		cout << endl;

		x.printans();
		cout << " - ";
		z.printans();
		cout << " = ";
		rat = x.sub(z);
		rat.printans();
		cout << " = ";
		rat.printnum();
		cout << endl;

		x.printans();
		cout << " * ";
		z.printans();
		cout << " = ";
		rat = x.mul(z);
		rat.printans();
		cout << " = ";
		rat.printnum();
		cout << endl;

		x.printans();
		cout << " / ";
		z.printans();
		cout << " = ";
		
		if(z.getDenominator() != 0) 
		{
			rat = x.div(z);
			rat.printans();
			cout << " = ";
			rat.printnum();
		}
		else
		{
			cout << "ERROR! DIVIDE BY ZERO  =  UNDEFINED!";
		}
		
		cout << endl << endl;

		cout << endl << endl; 
		cout << "Run Again (y/n)? ";//Ask to run again
		cin >> again;
		cout << endl; 
		fflush(stdin);
		cin.clear();
		
	}

	fflush(stdin);
	cin.clear();
	cout << endl << endl;
	cout << "Programmer: Adasuna" << endl << endl;//Display name
	cout << "Good bye! Press <Enter> to end the program...";//Have user exit 
	cin.get();
	return 0;

}

Rational::Rational()
{
	//Set number to one if nothing specified
	numerator = 1;
	denominator = 1;
}

Rational::Rational(int n, int d)
{
	numerator = n;
	denominator = d;
}

Rational::Rational(int n)
{
	//Set denominator to 1 if only one value passed in
	numerator = n;
	denominator = 1;
}

int Rational::GCD(int a, int b) 
{	
	if (b == 0)
	{
		return a;
	}		
	else
	{
		return GCD(b, a % b);
	}
}

void Rational::reduction()
{
	int temp = GCD(numerator, denominator);
	numerator = numerator / temp;
	denominator = denominator / temp;
}

void Rational::Denominator(int d)
{
	denominator = d;
}

void Rational::Numerator(int n)
{
	numerator = n;
}

int Rational::getDenominator() 
{
	return denominator;
}

int Rational::getNumerator() 
{
	return numerator;
}

void Rational::printans() 
{
	if(denominator == 1) 
	{
		cout << numerator;
	}
	else if(numerator == 0) 
	{
		cout << numerator;
	}
	else //if in form a/b
	{
		cout << numerator << "/" << denominator;
	}	
}

void Rational::printnum() 
{
	double temp = numerator;
	cout << temp / denominator;
}

Rational Rational::add(Rational temp) 
{
	int Denom = denominator * temp.getDenominator(); //get new denominator
	int Numon = (numerator * temp.getDenominator()) + (denominator * temp.getNumerator()); //calculate new numerator
	Rational back = Rational(Numon, Denom);
	back.reduction(); //reduce answer
	return back;
}

Rational Rational::sub(Rational temp) 
{
	int Denom = denominator * temp.getDenominator(); //get new denominator
	int Numon = (numerator * temp.getDenominator()) - (denominator * temp.getNumerator()); //calculate new numerator
	Rational back = Rational(Numon, Denom);
	back.reduction(); //reduce answer
	return back;
}

Rational Rational::mul(Rational temp) 
{
	int Denom = denominator * temp.getDenominator(); //get new denominator
	int Numon = numerator * temp.getNumerator(); //calculate new numerator
	Rational back = Rational(Numon, Denom);
	back.reduction(); //reduce answer
	return back;
}

Rational Rational::div(Rational temp) 
{
	int temp1 = temp.getDenominator();
	temp.Denominator(temp.getNumerator());
	temp.Numerator(temp1);
	int Denom = denominator * temp.getDenominator(); //get new denominator
	int Numon = numerator * temp.getNumerator(); //calculate new numerator
	Rational back = Rational(Numon, Denom);
	back.reduction(); //reduce answer
	return back;
}

[Adasuna]

Can anyone help me?