/* June 23, 1998 */
/* program to find the greatest common divisor */

#include <stdio.h>
#include <stdlib.h> /* provides function abs */

/*fucntion prototype */
void scan_fraction(int *nump, int *denomp);

main ()
{
	int n1, d1;
	int n2, d2;
	int q;
	int p;
	double r;
	int denom;
	int numer;
	int gcd;

	/* Get 2 fractions */	

	scan_fraction(&n1, &d1);
	scan_fraction(&n2, &d2);


        /* Computes numerator */
        numer = n1 * d2 + n2 * d1;

        /* Finds a common deminator */
        denom = d1 * d2;

	/* assign values */
        q = abs(numer);
        p = abs(denom);
        r = q%p;

	while (r != 0)
	{
		q = p;
		p = r;
		r = q%p;
	}

	gcd = p;

	/* display results */
	printf("The greatest common divisor, gcd, is %d\n", gcd);


}


/* function definition */

void
scan_fraction(int *nump, int *denomp)
{
        char slash;
        int status;
        int error;
        char discard;

        do {
                /* no errors detected yet */
                error= 0;

                /* get a fraction from the user */
                printf("Enter a common fraction as two integers separated ");
                printf("by a slash> ");
                status = scanf("%d %c%d", nump, &slash, denomp);

                /* validate the fraction */
                if (status < 3) {
                        error = 1;
                        printf("Invalid - please read directions 
carefully\n");
                } else if (slash != '/') {
                        error = 1;
                        printf("Invalid - separate numerator and 
denominator");
                        printf("by a slash (/) \n");
                } else if (*denomp <= 0) {
                        error = 1;
                        printf("Invalid - denominator must be positive\n");
                }

        /* discard extra input characters */
                do {
                 scanf("%c", &discard);
                } while (discard != '\n');
        } while (error);
}