5.7

Author: Heatwave

chapter-5-pointers-and-arrays/25.year-month-day.c

@@ -0,0 +1,87 @@
+#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}
+};
+
+int main()
+{
+	int day_of_year(int, int, int);
+	void month_day(int, int, int*, int*);
+
+	int day = day_of_year(2018, 8, 19);
+	printf("%d\n", day);
+
+	day = day_of_year(2018, 13, 19);
+	printf("%d\n", day);
+
+	day = day_of_year(2018, 12, 39);
+	printf("%d\n", day);
+
+	day = day_of_year(2018, 12, 0);
+	printf("%d\n", day);
+
+	int month;
+	month_day(2018, 231, &month, &day);
+	printf("%d, %d\n", month, day);
+
+	month_day(2018, -1, &month, &day);
+	printf("%d, %d\n", month, day);
+
+	month_day(2018, 1234, &month, &day);
+	printf("%d, %d\n", month, day);
+
+	month_day(2018, 365, &month, &day);
+	printf("%d, %d\n", month, day);
+
+	month_day(2018, 366, &month, &day);
+	printf("%d, %d\n", month, day);
+
+	month_day(2016, 366, &month, &day);
+	printf("%d, %d\n", month, day);
+
+	return 0;
+}
+
+int day_of_year(int year, int month, int day)
+{
+	int i, leap;
+	if (month < 1 || month > 12) {
+		printf("error: invalid month: %d\n", month);
+		return -1;
+	}
+
+	leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
+
+	if (day < 1 || day > daytab[leap][month]) {
+		printf("error: invalid day: %d\n", day);
+		return -1;
+	}
+
+	for (i = 1; i < month; i++)
+		day += daytab[leap][i];
+	return day;
+}
+
+void month_day(int year, int yearday, int *pmonth, int *pday)
+{
+	int i, leap;
+	leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
+	if (yearday < 1) {
+		printf("error: invalid yearday: %d\n", yearday);
+		return;
+	} else if (leap == 1 && yearday > 366) {
+		printf("error: invalid yearday: %d\n", yearday);
+		return;
+	} else if (leap == 0 && yearday > 365) {
+		printf("error: invalid yearday: %d\n", yearday);
+		return;
+	}
+
+	for (i = 1; yearday > daytab[leap][i]; i++)
+		yearday -= daytab[leap][i];
+	*pmonth = i;
+	*pday = yearday;
+}
+