下面這個程式使用C語言的結構體實現了分數的加減乘除四則運算，同時將結果最簡化。這裡為了簡化，將輸入值固定了，如果需要根據輸入進行計算，將main函式內的相應部分稍作修改即可。

#include <stdio.h>

struct fraction {
    int numerator;
    int denominator;
};

// 求解最大公約數
int find_gcd(int n1, int n2);

// 將分數化為最簡形式
struct fraction reduce_fraction(struct fraction f);

// 分數的四則運算
struct
 
 fraction add_fractions(struct fraction f1, struct fraction f2);
struct fraction subtract_fractions(struct fraction f1, struct fraction f2);
struct fraction multiply_fractions(struct fraction f1, struct fraction f2);
struct fraction divide_fractions(struct fraction f1, struct fraction f2);

int main(void
 
)
{

    struct fraction f = { 21, 3 };
    struct fraction f1 = { 8, 64 };
    struct fraction f2 = { 9, 711 };

    struct fraction reducedf = reduce_fraction(f);
    printf("%d/%d reduced to simplest terms: %d/%d\n", f.numerator,
        f.denominator, reducedf.numerator, reducedf.denominator);

    struct
 
 fraction addedf = add_fractions(f1, f2);
    printf("%d/%d + %d/%d = %d/%d\n", f1.numerator, f1.denominator,
        f2.numerator, f2.denominator, addedf.numerator, addedf.denominator);

    struct fraction subtractedf = subtract_fractions(f1, f2);
    printf("%d/%d - %d/%d = %d/%d\n", f1.numerator, f1.denominator,
        f2.numerator, f2.denominator, subtractedf.numerator,
        subtractedf.denominator);

    struct fraction multipliedf = multiply_fractions(f1, f2);
    printf("%d/%d * %d/%d = %d/%d\n", f1.numerator, f1.denominator,
        f2.numerator, f2.denominator, multipliedf.numerator,
        multipliedf.denominator);

    struct fraction dividedf = divide_fractions(f1, f2);
    printf("%d/%d / %d/%d = %d/%d\n", f1.numerator, f1.denominator,
        f2.numerator, f2.denominator, dividedf.numerator,
        dividedf.denominator);
    return 0;
}

int find_gcd(int n1, int n2)
{
    int temp;

    while (n1 != 0) {
        temp = n2 % n1;
        n2 = n1;
        n1 = temp;
    }

    return n2;
}

struct fraction reduce_fraction(struct fraction f)
{
    int gcd = find_gcd(f.numerator, f.denominator);
    f.numerator /= gcd;
    f.denominator /= gcd;
    return f;
}

struct fraction add_fractions(struct fraction f1, struct fraction f2)
{
    f1.numerator *= f2.denominator;
    f2.numerator *= f1.denominator;

    struct fraction result = {
        f1.numerator + f2.numerator,
        f1.denominator * f2.denominator
    };
    result = reduce_fraction(result);

    return result;
}

struct fraction subtract_fractions(struct fraction f1, struct fraction f2)
{
    f1.numerator *= f2.denominator;
    f2.numerator *= f1.denominator;

    struct fraction result = {
        f1.numerator - f2.numerator,
        f1.denominator * f2.denominator
    };
    result = reduce_fraction(result);

    return result;
}

struct fraction multiply_fractions(struct fraction f1, struct fraction f2)
{
    struct fraction result = {
        f1.numerator * f2.numerator,
        f1.denominator * f2.denominator
    };
    result = reduce_fraction(result);

    return result;
}
struct fraction divide_fractions(struct fraction f1, struct fraction f2)
{
    struct fraction result = {
        f1.numerator * f2.denominator,
        f1.denominator * f2.numerator
    };
    result = reduce_fraction(result);

    return result;
}