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#include <stdio.h>
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}};
/* Sets day of year from month and day */
int day_of_year(int year, int month, int day) {
int i, leap;
// leap year logic is only valid if this is true.
if (year < 1752) {
printf("error: invalid year\n");
return -1;
}
if (month < 1 || month > 12) {
printf("error: invalid month\n");
return -1;
}
if (day < 1) {
printf("error: invalid day\n");
return -1;
}
leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
for (i = 1; i < month; i++)
day += daytab[leap][i];
return day;
}
/* Sets month and day from day of year */
void month_day(int year, int yearday, int *pmonth, int *pday) {
int i, leap;
if (year < 0) {
*pmonth = *pday = 0;
printf("error: invalid year\n");
return;
}
if (yearday < 1) {
*pmonth = *pday = 0;
printf("error: invalid yearday\n");
return;
}
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;
}
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