第四章例4-2

#include<stdio.h>
#include<math.h>
int main(void)
{
int count,num;
double grade,total;

num=0;
total=0;
count=0;
printf("Enter grades:");
scanf("%lf",&grade);

while(grade>=0){
  total=total+grade;
  num++;
  if(grade<60)
   count++;
  scanf("%lf",&grade);
}
if(num!=0){
  printf("Grade average is %.2f\n",total/num);
  printf("Number of failures is %d\n",count);
}
else
  printf("Grade average is 0\n");