#include<stdio.h>
#define N 3
struct Student
{
    int num;
    char name[20];
    float score[3];
    float aver;
};

void input(struct Student stu[])
{
    int i;
    printf("请输入各学生的信息：学号、姓名、三门课成绩:\n");
    for (i = 0; i < N; i++)
    {
        scanf_s("%d%s%f%f", &stu[i].num, stu[i].name, 20, &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);
        stu[i].aver = (stu[i].score[0] + stu[i].score[1] + stu[i].score[2]) / N;
    }
}

struct Student max(struct Student stu[])
{
    int i;
    int m = 0;
    for (i = 0; i < N; i++)
        if (stu[m].aver < stu[i].aver)
            m = i;
    return stu[m];
}

void print(struct Student stud)
{
    printf("\n成绩最高的是:\n");
    printf("学号:%d\n姓名:%s\n三门课成绩:%5.1f,%5.1f,%5.1f\n平均成绩:%6.2f\n", stud.num, stud.name, stud.score[0], stud.score[1], stud.score[2], stud.aver);
}

int main()
{
    void input(struct Student stu[]);
    struct Student max(struct student stu[]);
    void print(struct Student stud);
    struct Student stu[N], *p;
    p = stu;
    input(p);
    print(max(p));
    return 0;
}

我这运行了一下，主函数中struct Student max(struct student stu[]); 应该首字母是大写吧，其他的没发现

void input(struct Student stu[])
{
    int i;
    printf("请输入各学生的信息：学号、姓名、三门课成绩:\n");
    for (i = 0; i < N; i++)
    {
        scanf("%d%s%f%f%f", &stu[i].num, stu[i].name,  &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]);    //
        stu[i].aver = (stu[i].score[0] + stu[i].score[1] + stu[i].score[2]) / 3;                               //3
    }
}

感觉参数数据类型写成struct Student *p比较好~不过这样写里面内容就要大改了~

你把void input (stu[])函数中的for中的scanf语句那行改为  scanf("%d%s%f%f%f", &stu[i].num, stu[i].name, &stu[i].score[0], &stu[i].score[1], &stu[i].score[2]); 这个就行了，你那句有几个错误，