#include<stdio.h>
#include<stdlib.h>
int main(){
    int a, b, i,j;
    printf("請輸入兩個數\n");
    scanf("%d%d", &a, &b);
    for (i = 2;i<=a;i++){
        if (a%i == 0 && b%i == 0)
        {
            j = i;
        }
    }
    printf("最大公約數為：%d", j);
    system("pause");
return 0;
}
 

2.輾轉相除法

#include<stdio.h>
#include<stdlib.h>
int main() {
    int a, b, c;
    printf("請輸入兩個數\n");
    scanf("%d%d", &a, &b);
    while (b!=0) {    //不用比較被除數和除數的大小
        c = a % b;
        a = b;
        b = c;
    }
    printf("最大公約數為：%d", a);
    system("pause");
    return 0;
}
 

3.更相減損法

#include<stdio.h>
int main() {
    int i = 0, j = 0, k = 0, a = 0, b = 0;
    scanf("%d%d", &i, &j);
    for (a = i,b = j;(a % 2 == 0) & (b % 2 == 0);) {
        a = a / 2;
        b = b / 2;
    }
    for (k=0;a!=b;) {
        while (a > b) {
            k = a - b;
            a = b;
            b = k;
        }
        if (a == b)
            break;
        k = b - a;
        a = a;
        b = k;
        }
    printf("%d與%d最大公約數為：%d\n",i,j,k);
    system("pause");
    return 0;
}
 

求最小公公倍數的三種方法