例4-2

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

    num=0;
    total=0;
    count=0;
    scanf_s("%lf",&grade);
    while(grade>=0){
        total=total+grade;
        num++;
        if(grade<60)
            count++;
        scanf_s("%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");

    return 0;
}