四、预习检查：填空，并注释"每空"填充的依据

1) 完成下列程序，该程序计算 10 名学生的平均成绩 

#include <stdio.h>
#include <string.h>
struct student {
    int num;
    char name[20];
    int score;
}; 
struct student stud[10];
int main(void)
{
    int   i , sum = 0 ;
    for(i = 0; i < 10; i++){
        scanf("%d%s%d ",&stud[i].num,stud[i].name, &stud[i].score);
        sum += stud[i].score;
    }
    printf("aver = %d 
", sum/10);
    return 0;
}

2) 下列程序读入时间数值，将其加 1 秒后输出，时间格式为：hh: mm: ss，即小时：分钟：秒，当小时等于 24 小时，置为 0。

#include<stdio.h>
struct { int hour, minute, second;} time;
int main(void)
{
    scanf("%d: %d: %d",    &time.hour, &time.minute, &time.second );
    time.second++;
    if( time.second == 60){
        time.minute++ ; 
        time.second = 0;
        if(time.minute == 60){
            time.hour++; 
            time.minute = 0;
            if( time.hour == 24 )
                time.hour = 0; 
        }
    }
    printf ("%d: %d: %d 
", time.hour, time.minute, time.second );
    return 0;
} 

3) 写出下面程序的运行结果，并简要描述原因。

struct s1{
    char c1, c2;
    int   n;
};
struct s2{
    int n; 
    struct s1 m;
} m = {1, {‘A’, ’B’, 2} };
int main(void)
{ 
    printf(“%d	%d	%c	%c
”, m.n, m.m.n, m.m.c1, m.m.c2);
    return 0;

1 2 A B

 4) 写出下面程序的运行结果，并简要描述原因

struct abc{    int a;    float b;    char *c; };
int main(void)
{
    struct abc x = {23,98.5,"wang"};
    struct abc *px = &x;
    printf("%d, %s, %.1f, %s 
", x.a, x.c, (*px).b, px->c );
    return 0;
}

23 wang 98.5 wang