C :

#include<stdio.h>
#include<string.h>

    struct student
    {

        int  id;                 //学号

        char name[20];   //姓名

        double score[3];  //三门课成绩，取值在0.0-100.0

        double aver;       //平均成绩，保留两位小数

    }a[100];
    double average(struct student *p);
    void shuru(int n);
    int high(struct student *p, int n);
int main()
{
    int n, i, h;
    double b[100], c;
    struct student *p;
    p = a;
    scanf("%d", &n);
    shuru(n);
    for(i=0; i<n; i++)
    {
        a[i].aver = average((p+i));
    }
    for(i=0; i<n; i++)
    {
        printf("%.2lf", a[i].aver);
        if(i<n-1)
            printf(" ");
    }
    printf("\n");
    h = high(p,n);
    printf("%d %s %.1lf %.1lf %.1lf %.2lf", a[h].id, a[h].name, a[h].score[0],  a[h].score[1], a[h].score[2], a[h].aver);

}

double average(struct student *p)
{
    int i;
    double sum = 0.0;
    for(i=0; i<3; i++)
    {
        sum += p->score[i];
    }
    return sum/3.0;
}
void shuru(int n)
{
    int i;

    for(i=0; i<n; i++)
    {
        scanf("%d", &a[i].id);
        scanf("%s", a[i].name);
        scanf("%lf", &a[i].score[0]);
        scanf("%lf", &a[i].score[1]);
        scanf("%lf", &a[i].score[2]);
    }

}

int high(struct student *p, int n)
{
    int i, highaver = 0;
    for(i=0; i<n;i++)
    {
        if((p+i)->aver > (p+highaver)->aver)
            highaver = i;
    }
    return highaver;
}

C++ :

#include<stdio.h>
#include<string.h>

    struct student
    {

        int  id;                 //学号

        char name[20];   //姓名

        double score[3];  //三门课成绩，取值在0.0-100.0

        double aver;       //平均成绩，保留两位小数

    }a[100];
    double average(struct student *p);
    void shuru(int n);
    int high(struct student *p, int n);
int main()
{
    int n, i, h;
    double b[100], c;
    struct student *p;
    p = a;
    scanf("%d", &n);
    shuru(n);
    for(i=0; i<n; i++)
    {
        a[i].aver = average((p+i));
    }
    for(i=0; i<n; i++)
    {
        printf("%.2lf", a[i].aver);
        if(i<n-1)
            printf(" ");
    }
    printf("\n");
    h = high(p,n);
    printf("%d %s %.1lf %.1lf %.1lf %.2lf", a[h].id, a[h].name, a[h].score[0],  a[h].score[1], a[h].score[2], a[h].aver);

}

double average(struct student *p)
{
    int i;
    double sum = 0.0;
    for(i=0; i<3; i++)
    {
        sum += p->score[i];
    }
    return sum/3.0;
}
void shuru(int n)
{
    int i;

    for(i=0; i<n; i++)
    {
        scanf("%d", &a[i].id);
        scanf("%s", a[i].name);
        scanf("%lf", &a[i].score[0]);
        scanf("%lf", &a[i].score[1]);
        scanf("%lf", &a[i].score[2]);
    }

}

int high(struct student *p, int n)
{
    int i, highaver = 0;
    for(i=0; i<n;i++)
    {
        if((p+i)->aver > (p+highaver)->aver)
            highaver = i;
    }
    return highaver;
}