#include<stdio.h>
int main(void)
{
    int year,month,day;
    int day_of_year(int year,int month,int day);
    printf("year,month,day:");
    scanf("%d%d%d",&year,&month,&day);
    day_of_year(year,month,day);
    printf("days of year:%d\n",day);
    return 0;
}
int day_of_year(int year,int month,int day)
{
    int k,leap;
    int tab[2][3]={
        {0,31,28,31,30,31,30,31,31,30,31,30,31},
        {0,31,29,31,30,31,30,31,31,30,31,30,31}
    };
    leap=(year%4==0&&year%100!=0||year%400==0);
    for(k=1;k<month;k++)
        day=day+tab[leap][k];
    return day;
}

手机上观察tab2，13

数组赋值越界了

·
·
day_of_year(year,month,day); /* 没接收day_of_year函数的反回值 */
    printf("days of year:%d\n",day);
    return 0;
}
int day_of_year(int year,int month,int day)
{
    int k,leap;
    int tab[2][3]={          /* 数组定义小了 */
·
·

#include<stdio.h>
int main(void)
{
    int year,month,day;
    int day_of_year(int year,int month,int day);
    printf("year,month,day:");
    scanf("%d%d%d",&year,&month,&day);
    
    printf("days of year:%d\n",day_of_year(year,month,day));   /* 要不直接放在printf里 */
    return 0;
}
int day_of_year(int year,int month,int day)
{
    int k,leap;
    int tab[2][13]={              /* 每行13个元素 */
    {0,31,28,31,30,31,30,31,31,30,31,30,31},
        {0,31,29,31,30,31,30,31,31,30,31,30,31}
    };
    leap=(year%4==0&&year%100!=0||year%400==0);
    for(k=1;k<month;k++)
        day=day+tab[leap][k];
    return day;
}

int tab[2][3]={
        {0,31,28,31,30,31,30,31,31,30,31,30,31},
        {0,31,29,31,30,31,30,31,31,30,31,30,31}
这里太夸张了吧

//任意输一个日期，判断是当年的第几天
#include<stdio.h>
main()
{
    int day_of_year(int day,int month,int year);
    int day,month,year;
    printf("input year,month,day:\n");
    scanf("%d%d%d",&year,&month,&day);
    printf("%d年%d月%d日是当年的第%d天\n",year,month,day,
        day_of_year(day,month,year));
}
int day_of_year(int day,int month,int year)
{
    int k,leap,monthday[2][12]={
        {31,29,31,30,31,30,31,31,30,31,30,31},
        {31,28,31,30,31,30,31,31,30,31,30,31}};
    leap=(year%4==0 && year%100 || year%400==0);
    for(k=0;k<month-1;k++)
        day+=monthday[leap][k];
    return day;
}
思路属于抄袭你的，只是小修了一下，仅供草考，嘿嘿…

哇...活了

瞧瞧

for(k=0;k<month-1;k++)
        day+=monthday[leap][k];
问 一下！这枚看懂!for语句里为什么是k<month-1啊？还有这的day+=monthday[leap][k];这一句的前半段我还能看懂，后半段怎么解释啊！劳驾解释一下！

#include<stdio.h>

int main()
{
    int day_of_year(int day,int month,int year);
    int day,month,year;
    printf("input year,month,day:\n");
    scanf("%d%d%d",&year,&month,&day);
    printf("%d-%d-%d %d\n",year,month,day,day_of_year(day,month,year));
}

int day_of_year(int day,int month,int year)
{
    int k,leap,monthday[2][12]={
        {31,28,31,30,31,30,31,31,30,31,30,31},
        {31,29,31,30,31,30,31,31,30,31,30,31}
                                };
    leap=((year%4==0&&year%100!=0)||year%400==0);
    for(k=0;k<month-1;k++)
   ｛
       day+=monthday[leap][k];
    ｝
    return day;
}

在    for(k=0;k<month-1;k++)
   ｛
       day+=monthday[leap][k];
    ｝
k对应12，因为是从K=0开始，即当k=0时已经为1月，k=11是为12月
leap=((year%4==0&&year%100!=0)||year%400==0);当leap==1时为闰年