根据年月日计算今天是一年中的第几天
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} };
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; }