c语言问题,生成随机数,很简单的问题..

#include<stdio.h>
#include<stdlib.h>
main()
{
int i,a,b,c,s=0;
rand();
for(i=0;i<=9;i++)
{
do {a=20+ rand()%100; //这里怎么该?
b=2+ rand()%10;}//还有这里
while(a%b!=0);
printf("%d/%d=",a,b);
scanf("%d",&c);
if(a/b==c)
{
printf("right!\n");
s+=10;
}
else printf("error!\n");
}
printf("the result is%d\n",s);
}

#define rrand(min, max) (rand() % ((max) - (min)) + (min))

然后rrand(2, 10)
rrand(10, 200)