ex.11.11.c

// Program to determine tomorrow's date

#include <stdio.h>
#include <stdbool.h>

struct date
{
	int month;
	int day;
	int year;
};

// Function to calculate tomorrow's date

void dateUpdate (struct date *today)
{
	int numberOfDays (struct date d);

	if ( today->day != numberOfDays (*today) ) {
		today->day++;
	}
	else if ( today->month == 12 ) {		// end of year
		today->day = 1;
		today->month = 1;
		today->year++;
	}
	else {								// end of month
		today->day = 1;
		today->month++;
	}
}

// Function to find the number of days in a month

int numberOfDays (struct date d)
{
	int		days;
	bool	isLeapYear (struct date d);

	const int daysPerMonth[12] = {
		31, 28, 31, 30, 31, 30,
		31, 31, 30, 31, 30, 31
	};

	if ( isLeapYear (d) == true && d.month == 2 )
		days = 29;
	else
		days = daysPerMonth[d.month - 1];

	return days;
}

// Function to determine if it's a leap year

bool isLeapYear (struct date d)
{
	bool leapYearFlag;

	if ( (d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0 )
		leapYearFlag = true;	// It's a leap year
	else
		leapYearFlag = false;	// Not a leap year

	return leapYearFlag;
}

int main (void)
{
	void dateUpdate (struct date *today);
	struct date thisDay;

	printf ("Enter today's date (mm dd yyyy): ");
	scanf  ("%i%i%i", &thisDay.month, &thisDay.day, &thisDay.year);

	dateUpdate (&thisDay);

	printf ("Tomorrow's date is %i/%i/%.2i.\n", thisDay.month,
			thisDay.day, thisDay.year % 100);

	return 0;
}