完整程式碼

#include <stdio.h>

int main(void){
	int A, B, i, gcd;
	scanf("%d %d", &A, &B);
	for(i=A; i>=1; i--){
		if(A%i == 0 && B%i ==0){
			gcd = i;
			break;
		}
	}
	printf("%d\n", gcd);
	printf("%d", A*B/gcd);
	
	return 0;
}

While迴圈解

#include <stdio.h>

int main(void){
    int a, b, r, num1, num2;

    scanf("%d %d", &a, &b);
    num1=a; num2=b;

    while(b!=0){
        r = a%b;
        a = b;
        b = r;
    }
    printf("%d\n%d", a, num1*num2/a);
    return 0;
}

遞迴函式

#include <stdio.h>
int gcd(int a, int b);
int lcm(int a, int b);
int main(void){
    int a, b;

    scanf("%d %d", &a, &b);

	printf("%d\n",gcd(a,b));
 	printf("%d",lcm(a,b));
 	
 	return 0;
}
// GCD, LCM 遞迴函式
int gcd(int a, int b){
 	if(b==0){
 		return a;
 	}else{
 		return gcd(b, a%b);
    }
}int lcm(int a, int b){
 	return (a*b/gcd(a,b));
}

輸出結果

參考資料：TQC+ C第2版