随机数产生

#include <stdio.h> 
#include <stdlib.h>     
#include <time.h>

int main()
{
int a, b = 0, c;

srand(time(NULL)); 
a = rand()%101;

do
{
printf("请输入数字：\n");
scanf("%d", &c);
b++;

if( c > a )
   printf("大了\n");
else if( c < a )
   printf("小了\n");

} 
while(c!= a);

printf("对了,成绩是：");

if( b < 3 )
{ switch(b)
{
case 1:printf("100\n");break;
case 2:printf("90\n");break;
case 3:printf("80\n");break;
}
}

else if( b < 7 )
{
switch(b)
{
case 4:printf("75\n");break;
case 5:printf("70\n");break;
case 6:printf("65\n");break;
     case 7:printf("60\n");break;
}
}
else
printf("不及格\n");
return 0;
}