日期转换

static char daytab[2][13] = {
    {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}
};
/* 将某日某月的日期表示形式转换为某年中第几天的表示形式*/
int day_of_year(int year, int month, int day)
{
    int i, leap;
    leap = year%4 == 0 && year%100 != 0 || year%400 == 0;
    for (i = 1; i < month; i++)
        day += daytab[leap][i];
    return day;
}
/*将某年中第几天的日期表示形式转换为某月某日的表示形式*/
int month_day(int year, int yearday, int *pmonth, int *pday)
{
    int i, leap;
    leap = year%4 == 0 && year%100 != 0 || year%400 == 0;
    for (i = 1; yearday > daytab[leap][i]; i++)
        yearday -= daytab[leap][i];
    *pmonth = i;
    *pday = yearday;
}