/*
 * Program demonstrating use of struct to represent fractions.
 */
#include <stdio.h>
#include <stdlib.h>

/* struct representing a fraction */
struct fraction {
    int numer;
    int denom;
};

/* function declarations -- comments below with definitions */
void init_fraction(struct fraction * f, int numer, int denom);
int print_fraction(struct fraction * f);
int gcd(int a, int b);
void simplify_fraction(struct fraction * f);
/* function declarations for add, subtract, multiply, divide go here */

/* main program */
int main(void) {

    struct fraction f1;
    struct fraction f2;
    struct fraction result;
    int numer_in;
    int denom_in;

    printf("enter numerator and denominator for first fraction:\n");
    if (scanf("%d %d", &numer_in, &denom_in) != 2) {
        fprintf(stderr, "values must be numeric\n");
        return EXIT_FAILURE;
    }
    init_fraction(&f1, numer_in, denom_in);
    printf("enter numerator and denominator for second fraction:\n");
    if (scanf("%d %d", &numer_in, &denom_in) != 2) {
        fprintf(stderr, "values must be numeric\n");
        return EXIT_FAILURE;
    }
    init_fraction(&f2, numer_in, denom_in);

    printf("input fractions:\n");
    printf("f1 = ");
    print_fraction(&f1);
    printf("\n");
    printf("f2 = ");
    print_fraction(&f2);
    printf("\n");

    add(&f1, &f2, &result);
    printf("f1 + f2 = ");
    print_fraction(&result);
    printf("\n");

    subtract(&f1, &f2, &result);
    printf("f1 - f2 = ");
    print_fraction(&result);
    printf("\n");

    multiply(&f1, &f2, &result);
    printf("f1 * f2 = ");
    print_fraction(&result);
    printf("\n");

    divide(&f1, &f2, &result);
    printf("f1 / f2 = ");
    print_fraction(&result);
    printf("\n");

    return EXIT_SUCCESS;
}

/* 
 * initialize instance of "fraction" structure.
 */
void init_fraction(struct fraction * f, int numer, int denom) {
    /* another syntax
    (*f).numer = numer;
    (*f).denom = denom;
    */
    f->numer = numer;
    f->denom = denom;
    simplify_fraction(f);
}

/* 
 * "print" instance of "fraction" structure to standard output, in the
 *   form numerator/denominator.
 *
 * returns return value from printf (which is usually ignored, but
 *   return for consistency, or just in case caller wants it).
 */
int print_fraction(struct fraction * f) {
    return printf("%d/%d", f->numer, f->denom);
}

/*
 * find greatest common divisor of two non-negative integers.
 */
int gcd(int a, int b) {
    /* euclid's algorithm */
    if (b == 0) return a;
    else return gcd(b, a % b);
}

/*
 * "simplify" fraction -- reduce to lowest terms.  
 * (Not implemented.)
 */
void simplify_fraction(struct fraction * f) {
}