// Tony Zulani's Extra Credit
// Program Algorithm determines the greatest common divisor of two positive
// integers.  It works out according to Euclid's algorithm.  The data is taken
// from a file of values, and the output is also written to a file.

#include <iostream.h>
#include <fstream.h>

int FindGCD(int, int);
// Determines the GCD of two numbers

int main()
{
	int value1;				//the first value of a pair of numbers
	int value2;				//the second value of a pair of numbers
	ifstream dataFile;	//input file stream
	ofstream gcdList;		//output file stream

	dataFile.open("data.in");
	gcdList.open("data.out");

	dataFile >> value1 >> value2; 	//priming read of two values

	while(dataFile)
	{
		gcdList << "The GCD of the numbers " << value1 << " and " << value2
		 << " is " << FindGCD(value1, value2) << endl;

		dataFile >> value1 >> value2;	//read next two values
	}
	return 0;
}



// **************************************************************************

int FindGCD(int num1, int num2)
//Pre: Two numbers have been input from a file stream
//Post: The greatest common divisor of the two numbers is found and returned
//		  to main.
{
	int r;					//remainder from division of the two numbers
	int GCD;					//greatest common divisor returned to main
	int temp;				//temporary variable in case num1 > num2

	if (num1 > num2)
	{
		temp = num1;		//num1 copied into temp;
		num1 = num2;		//num2 copied into num1;
		num2 = temp;		//temp copied into num2; now, num1 <= num2
	}

	r = num2 % num1;     //determine the remainder
	if (r == 0)
		GCD = num1; 		//num1 is GCD
	else
	{
		while (r != 0)
		{
			num2 = num1;
			num1 = r;
			r = num2 % num1;
		}
		GCD = num1;   		//num1 is GCD
	}
	return GCD;
}