下面是我的程序
#include <stdio.h>
#include <stdlib.h>

struct stu
{
    char name[20];
    int f;
    char d;
    struct stu *pnext;
};
struct stu* newhear()     //为所有学生姓名和成绩进行初始化
{
    struct stu  *ph, *pn, *pe;
    int c, d;
    printf("请输入学生总人数（不超过50人）：");
    scanf_s("%d", &d, 4);                             //输入学生总人数
    pe = (struct stu*)malloc(sizeof(struct stu));    //为pe分配内存       也是第一个节点                    
    ph = pn = pe;                                    //使第一个学生成为头
    for (c = 0; c < d; c++)
    {
        printf("请输入第%d个学生的姓名\n",c+1);
        scanf_s("%s", pn->name, 20); //输入第一个学生的姓名和成绩
        printf("成绩;\n");
        scanf_s("%d",&pn->f, 4);
        if (c < (d - 1))
        {   
            pe = (struct stu*)malloc(sizeof(struct stu));
            pn->pnext = pe;
            pn = pe;
        }
    }
    pn->pnext = NULL;
    return ph;     //返回链表的开头，便于后面调用
}
double Average(struct stu *pe)
{
    struct stu *pa ;
    pa = pe;
    int a;
    int b;
    for(a = 1,b=0; pa != NULL; a++);
    {
        b = pa->f+b;                           
        pa = pa->pnext;
    }
    b = b / a;
    return b;
}

void garde(struct stu *pe,double a)
{
    struct stu *pg = pe;
    while (pg != NULL)
    {
        if ((a + 10) < pg->f)
            pg->d = 'A';
        if ((pg->f>=(a-10))&& (pg->f<=(a+10)));
            pg->d = 'B';
        if(pg->f<(a-10))
            pg->d = 'C';
        pg = pg->pnext;
    }
}
main()
{
    struct stu *pe;
    double a;
    pe = newhear(); //接受链表的头
    a=Average(pe);    //求平均分数
    garde(pe,a);     //调用打分系统
    system("pause");

}