#include<stdio.h>
struct Data{
    int year;
    int month;
    int day;
    char name[20];
    int age;
};
struct Data sd[5]={{2021,9,1,"zhangshan",18},{2021,9,1,"lisi",19},{2020,9,20,"wanghu",20},
{2020,9,23,"liubin",20},{2019,9,30,"hudayong",21}};
int main()
{
    void input(struct Data sd[5]);
    struct Data*p;
    printf("年. 月 .日 .姓名 年龄. 平均年龄\n");
    for(p=sd;p<sd+5;p++)
        printf("%4d %d %d %-20s %2d %d\n",p->year,p->month,p->day,p->nam,p->age,p->arrage);
    return 0;
}
void input(struct Data sd[5])
{
    sd[5].arrage=(sd[5].a[0]+sd[5].a[1]+sd[5].a[2]+sd[5].a[3]+sd[5].a[4])/3;
}

敬告：
1.学好汉语，让别人知道你在说什么
2.学点英语，知道编程器提示的是什么

[此贴子已经被作者于2021-1-13 22:20编辑过]

刚学C，看不明白

看编译器的错误提示
你的arrage和a[]哪来的？在哪里声明了？

说实话，看不懂想怎样输出

#include <stdio.h>

struct Data {
    int year;
    int month;
    int day;
    char name[20];
    int age;
};

double average_age( const struct Data sd[], size_t n );

int main( void )
{
    struct Data sd[5] = { {2021, 9,  1, "zhangshan", 18}
                        , {2021, 9,  1, "lisi",      19}
                        , {2020, 9, 20, "wanghu",    20}
                        , {2020, 9, 23, "liubin",    20}
                        , {2019, 9, 30, "hudayong",  21} };

    printf("%-4s %2s %2s %-20s %s\n", "年", "月", "日", "姓名", "年龄" );
    for( size_t i=0; i!=sizeof(sd)/sizeof(*sd); ++i )
        printf( "%4d %2d %2d %-20s %4d\n", sd[i].year, sd[i].month, sd[i].day, sd[i].name, sd[i].age );
    printf( "平均年龄: %.1f\n", average_age(sd,sizeof(sd)/sizeof(*sd)) );
}

double average_age( const struct Data sd[], size_t n )
{
    double sum = 0;
    for( size_t i=0; i!=n; ++i )
        sum += sd[i].age;
    return n!=0 ? sum/n : 0;
}