#include <iostream.h> // for cerr

class rational
{	// represents a rational number in the form numerator / denominator.
	// conditions maintained in class:
	//   denominator > 0, sign maintained in numerator
	public:
		// methods
			rational (); // mirrors original constructor
				// declares a rational number and initializes it to 0/1
			rational (int numerator, int denominator);
				// declares and initializes the rational number
			void initialize (int numerator, int denominator, bool &ok);
				// initializes the rational number.  ok= (denominator > 0)
			int returnNumerator ();   // returns the numerator of the rational number
			int returnDenominator (); // returns the denominator of the rational number
			void reduce ();
			void add (rational fraction);
			void sub (rational fraction);
			void mul (rational fraction);
			void div (rational fraction);
			bool operator== (rational fraction);
	private:
		int numer, denom;
}; // class rational

bool rational::operator== (rational fraction) {
	return (numer==fraction.numer && denom==fraction.denom);
} // rational::operator==

rational::rational()
{	bool ok;
	initialize (0, 1, ok);
} //rational::rational

rational::rational (int numerator, int denominator)
{	bool ok;
	initialize (numerator, denominator, ok);
	if (!ok)
		cerr <<"Error: denominator is " <<denominator;
						// writes an error message to standard error stream
} // rational::rational

void rational::initialize (int numerator, int denominator, bool &ok)
{	if (denominator <= 0)
		ok= false;
	else
	{	ok= true;
		numer= numerator;
		denom= denominator;
	} //if
} // rational::rational

int rational::returnNumerator ()
{	return (numer);
} // rational::returnNumerator

int rational::returnDenominator ()
{	return (denom);
} // rational::returnDenominator

void rational::reduce () {
	int GCD (int, int);
	int x= GCD (numer, denom);
	numer /= x;
	denom /= x;
} // rational::reduce

int GCD (int a, int b)
// determines the greatest common divisor of a and b
// note: better algorithms exist!
{	int possCD, GCDsoFar= 1;
	for (possCD= 2; possCD <= a; ++possCD)
		if ((a % possCD == 0) && (b % possCD == 0))
			GCDsoFar= possCD;
	return (GCDsoFar);
} // GCD

void rational::add (rational fraction){
	void makeCommonDen (rational &, rational &);
	makeCommonDen (*this, fraction);
	numer= numer + fraction.numer;
	reduce();
} // rational::add*

void rational::sub (rational fraction){
	void makeCommonDen (rational &, rational &);
	makeCommonDen (*this, fraction);
	numer= numer - fraction.numer;
	reduce();
} // rational::sub*

void rational::mul (rational fraction){
	void makeCommonDen (rational &, rational &);
	makeCommonDen (*this, fraction);
	numer= numer * fraction.numer;
	reduce();
} // rational::mul

void rational::div (rational fraction){
	void makeCommonDen (rational &, rational &);
	makeCommonDen (*this, fraction);
	numer= numer / fraction.numer;
	reduce();
} // rational::div

void makeCommonDen (rational &fr1, rational &fr2)
{	bool ok;
	int commonDen= fr1.returnDenominator() *  fr2.returnDenominator() *
									GCD (fr1.returnDenominator(), fr2.returnDenominator());
	fr1.initialize (fr1.returnNumerator() * commonDen / fr1.returnDenominator(),
									commonDen, ok);
	fr2.initialize (fr2.returnNumerator() * commonDen / fr2.returnDenominator(),
									commonDen, ok);
} // makeCommonDen

void printFract(){
	cout<<numer<<endl<<"----"<<endl<<denom<<endl;

}//printFract

#include <iostream.h>

void main () {
	rational fraction1 (6, 14), fraction2 (-1, 7), fraction3;
	fraction1.reduce();
	cout <<fraction1.returnNumerator () <<"/" <<fraction1.returnDenominator() <<endl;
		// outputs: 3/7
	fraction1.add (fraction2);
	cout <<fraction1.returnNumerator () <<"/" <<fraction1.returnDenominator() <<endl <<endl;
		// outputs: 2/7
	if (fraction1==fraction2)
		cout <<"Equal." <<endl;
	else
		cout <<"Not equal." <<endl;

	printFract();
}

class rational
{
    ///.......
  private:
    int numer, denom;

    friend void printFract();
};