calculator.c

#include <stdio.h>
#include <stdlib.h>
int get_1st_weekday(int year)
{
	int d;
	d = (((year - 1) * 365) + ((year - 1) / 4) - ((year - 1) / 100) + ((year) / 400) + 1) % 7;
	return d;
}
int main()
{
	system("Color 3F");
	int year, month, day, daysInMonth, weekDay = 0, startingDay;
	printf("\nEnter your favourite year:");
	scanf("%d", &year);
	char *months[] = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October ", " November ", " December "};
	int monthDay[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)
		monthDay[1] = 29;
	startingDay = get_1st_weekday(year);
	for (month = 0; month < 12; month++)
	{
		daysInMonth = monthDay[month];
		printf("\n\n---------------%s-------------------\n", months[month]);
		printf("\n Sun Mon Tue Wed Thurs Fri Sat\n");
		for (weekDay = 0; weekDay < startingDay; weekDay++)
			printf(" ");
		for (day = 1; day <= daysInMonth; day++)
		{
			printf("%5d", day);
			if (++weekDay > 6)
			{
				printf("\n");
				weekDay = 0;
			}
			startingDay = weekDay;
		}
	}
}