#include<stdio.h>
int main()
{
    int a,b,y=1,n,a1,b1;
    printf("请输入两个正整数:");
    scanf("%d%d",&a,&b);
    a1=a;
    b1=b;
    for(;y!=0;)
    {
        y=a%b;
        a=b;
        b=y;}
    n=a1*b1/b;
    printf("最大公因数为：%d\n最小公倍数为：%d\n",b,n);
    return 0;
}

    for(;;)
        {
            y=a%b;
            if(y==0) break;
            a=b;
            b=y;
        }

代码要清晰无杂质

#include <stdio.h>

unsigned gcd( unsigned a, unsigned b )
{
    for( ; b!=0; )
    {
        unsigned t = a%b;
        a = b;
        b = t;
    }
    return a;
}

int main( void )
{
    unsigned a, b;
    printf( "请输入两个正整数: " );
    scanf( "%u%u", &a, &b );

    unsigned g = gcd( a, b );
    unsigned l = a/g*b;
    printf( "最大公因数为：%d\n", g );
    printf( "最小公倍数为：%d\n", l );
}