C语言 计算班级平均成绩以及不及格的人数

#include <stdio.h>
int main()
{
    int num,bujige;
    double grade,total;
    num=0;
    bujige=0;
    total=0;
    printf("Enter grade:");
    scanf("%lf",&grade);
    while(grade>0)
    {
        total+=grade;
        num++;
        if(grade<60)
            bujige++;
            scanf("%lf",&grade);
    }
        if(num!=0)
        {
            printf("Grade average is%.2lf\n",total/num);
            printf("Number of failures is%d\n",bujige);
        }
        else
            printf("Grade average is 0\n");
}

这个是以负数结尾的，输入成绩 如90 58 62 58 41 23 -1；以负数来结尾。