Calandar generator (based on snippet by Joe) printing a calendar for any year source code

This snippet submitted by Tyler Veness on 2011-11-20. It has been viewed 33166 times.
Rating of 6.7 with 509 votes
#include <iostream>
#include <iomanip>

bool isLeapYear( unsigned int& ); //checks if 'year' is leap year
unsigned int firstDayOfJanuary( unsigned int& year );
unsigned int numOfDaysInMonth( unsigned int , unsigned int& ); // takes the number of the month, and 'year' as arguments
void printHeader( unsigned int ); //takes the number of the month, and the first day, prints, and updates
void printMonth( unsigned int , unsigned int& ); //takes number of days in month, and reference to 'firstDayInCurrentMonth' so it updates after every call
void skip( unsigned int ); //prints the specified amount of spaces

int main() {
	unsigned int year , firstDayInCurrentMonth;
	std::cout << "Calendar year? ";
	std::cin >> year;
	std::cout << "\n";
	firstDayInCurrentMonth = firstDayOfJanuary( year );
	skip(9);
	std::cout << year << "\n";
	for ( unsigned int currentMonth = 1 ; currentMonth <= 12 ; currentMonth++ ) {
		printHeader( currentMonth );
		printMonth( numOfDaysInMonth( currentMonth , year ) , firstDayInCurrentMonth );
		std::cout << "\n\n\n";
	}
	std::cout << "Press Enter to Exit...";
	std::cin.ignore();
	std::cin.get();
}

bool isLeapYear( unsigned int& year ) { //if number is multiple of 4 and is either multiple of 400 or not multiple of 100, is leap year
	return ( year % 4 == 0 ) && ( year % 100 != 0 || year % 400 == 0 );
}

unsigned int firstDayOfJanuary( unsigned int& year ) {
	/* "( 97 * year - 97 ) / 400" is the simplification of:

	x1 = (year - 1)/ 4;
	x2 = (year - 1)/ 100;
	x3 = (year - 1)/ 400;
	day_start = (year + x1 - x2 + x3) % 7;

	after each value is plugged in
	 */

	return ( year + ( 97 * year - 97 ) / 400 ) % 7;
}

unsigned int numOfDaysInMonth( unsigned int m , unsigned int& year ) {
	if ( m == 2 )
		return isLeapYear( year ) ? 29 : 28; //if month is February, return correct number based on whether it is leap year
	else
		return 30 + ( m % 2 ); //otherwise return 31 if month number is odd, 30 if month number is even
}

void printHeader( unsigned int m ) {
	skip( 7 );

	if ( m == 1 ) std::cout << "January";
	else if ( m == 2 ) std::cout << "February";
	else if ( m == 3 ) std::cout << "March";
	else if ( m == 4 ) std::cout << "April";
	else if ( m == 5 ) std::cout << "May";
	else if ( m == 6 ) std::cout << "June";
	else if ( m == 7 ) std::cout << "July";
	else if ( m == 8 ) std::cout << "August";
	else if ( m == 9 ) std::cout << "September";
	else if ( m == 10 ) std::cout << "October";
	else if ( m == 11 ) std::cout << "November";
	else if ( m == 12 ) std::cout << "December";

	std::cout << "\n S  M  T  W  T  F  S" << "\n";
	std::cout << "____________________" << "\n";
}

void skip( unsigned int i ) {
	while ( i > 0 ) {
		std::cout << " ";
		i--;
	}
}

void printMonth( unsigned int numDays, unsigned int &weekDay ) {
	skip( 3 * weekDay ); //3 is width of a calendar number
	for ( unsigned int day = 1 ; day <= numDays ; day++ ) {
		std::cout << std::setw(2) << day << " ";

		if ( weekDay == 6 ) {
			std::cout << "\n";
			weekDay = 0;
		}
		else
			weekDay++;
	}
}
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