Task: Calendar

C: #include <stdio.h>
#include <stdlib.h>
#include <string.h>

int width = 80, year = 1969;
int cols, lead, gap;

const char *wdays[] = { "Su", "Mo", "Tu", "We", "Th", "Fr", "Sa" };
struct months {
	const char *name;
	int days, start_wday, at;
} months[12] = {
	{ "January",	31, 0, 0 },
	{ "February",	28, 0, 0 },
	{ "March",	31, 0, 0 },
	{ "April",	30, 0, 0 },
	{ "May",	31, 0, 0 },
	{ "June",	30, 0, 0 },
	{ "July",	31, 0, 0 },
	{ "August",	31, 0, 0 },
	{ "September",	30, 0, 0 },
	{ "October",	31, 0, 0 },
	{ "November",	30, 0, 0 },
	{ "December",	31, 0, 0 }
};

void space(int n) { while (n-- > 0) putchar(' '); }

void init_months()
{
	int i;

	if ((!(year % 4) && (year % 100)) || !(year % 400))
		months[1].days = 29;

	year--;
	months[0].start_wday
		= (year * 365 + year/4 - year/100 + year/400 + 1) % 7;

	for (i = 1; i < 12; i++)
		months[i].start_wday =
			(months[i-1].start_wday + months[i-1].days) % 7;

	cols = (width + 2) / 22;
	while (12 % cols) cols--;
	gap = cols - 1 ? (width - 20 * cols) / (cols - 1) : 0;
	if (gap > 4) gap = 4;
	lead = (width - (20 + gap) * cols + gap + 1) / 2;
        year++;
}

void print_row(int row)
{
	int c, i, from = row * cols, to = from + cols;
	space(lead);
	for (c = from; c < to; c++) {
		i = strlen(months[c].name);
		space((20 - i)/2);
		printf("%s", months[c].name);
		space(20 - i - (20 - i)/2 + ((c == to - 1) ? 0 : gap));
	}
	putchar('\n');

	space(lead);
	for (c = from; c < to; c++) {
		for (i = 0; i < 7; i++)
			printf("%s%s", wdays[i], i == 6 ? "" : " ");
		if (c < to - 1) space(gap);
		else putchar('\n');
	}

	while (1) {
		for (c = from; c < to; c++)
			if (months[c].at < months[c].days) break;
		if (c == to) break;

		space(lead);
		for (c = from; c < to; c++) {
			for (i = 0; i < months[c].start_wday; i++) space(3);
			while(i++ < 7 && months[c].at < months[c].days) {
				printf("%2d", ++months[c].at);
				if (i < 7 || c < to - 1) putchar(' ');
			}
			while (i++ <= 7 && c < to - 1) space(3);
			if (c < to - 1) space(gap - 1);
			months[c].start_wday = 0;
		}
		putchar('\n');
	}
	putchar('\n');
}

void print_year()
{
	int row;
	char buf[32];
	sprintf(buf, "%d", year);
	space((width - strlen(buf)) / 2);
	printf("%s\n\n", buf);
	for (row = 0; row * cols < 12; row++)
		print_row(row);
}

int main(int c, char **v)
{
	int i, year_set = 0;
	for (i = 1; i < c; i++) {
		if (!strcmp(v[i], "-w")) {
			if (++i == c || (width = atoi(v[i])) < 20)
				goto bail;
		} else if (!year_set) {
			if (!sscanf(v[i], "%d", &year) || year <= 0)
				year = 1969;
			year_set = 1;
		} else
			goto bail;
	}

	init_months();
	print_year();
	return 0;

bail:	fprintf(stderr, "bad args\nUsage: %s year [-w width (>= 20)]\n", v[0]);
	exit(1);
}


C++: #include <windows.h>
#include <iostream>


using namespace std;



class calender
{
public:
    void drawCalender( int y )
    {
	year = y;
	for( int i = 0; i < 12; i++ )
	    firstdays[i] = getfirstday( i );

	isleapyear();
	build();
    }

private:
    void isleapyear()
    {
	isleap = false;

	if( !( year % 4 ) )
	{
	    if( year % 100 ) isleap = true;
	    else if( !( year % 400 ) ) isleap = true;
	}
    }

    int getfirstday( int m )
    {
	int y = year;

	int f = y + 1 + 3 * m - 1;
	m++;
	if( m < 3 ) y--;
	else f -= int( .4 * m + 2.3 );

	f += int( y / 4 ) - int( ( y / 100 + 1 ) * 0.75 );
	f %= 7;

	return f;
    }

    void build()
    {
	int days[] = { 31, isleap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
	int lc = 0, lco = 0, ystr = 7, start = 2, fd = 0, m = 0;
	HANDLE h = GetStdHandle( STD_OUTPUT_HANDLE );
	COORD pos = { 0, ystr };
	draw();

	for( int i = 0; i < 4; i++ )
	{
	    for( int j = 0; j < 3; j++ )
	    {
		int d = firstdays[fd++], dm = days[m++];
		pos.X = d * 3 + start;
		SetConsoleCursorPosition( h, pos );

		for( int dd = 0; dd < dm; dd++ )
		{
		    if( dd < 9 ) cout << 0 << dd + 1 << " ";
		    else cout << dd + 1 << " ";

		    pos.X += 3;
		    if( pos.X - start > 20 )
		    {
			pos.X = start; pos.Y++;
			SetConsoleCursorPosition( h, pos );
		    }
		}

		start += 23;
		pos.X = start; pos.Y = ystr;
		SetConsoleCursorPosition( h, pos );
	    }
	    ystr += 9; start = 2;
	    pos.Y = ystr;
	}
    }

    void draw()
    {
	system( "cls" );
	cout << "+--------------------------------------------------------------------+" << endl;
	cout << "|                              [SNOOPY]                              |" << endl;
	cout << "|                                                                    |" << endl;
	cout << "|                             == " << year << " ==                             |" << endl;
	cout << "+----------------------+----------------------+----------------------+" << endl;
	cout << "|       JANUARY        |       FEBRUARY       |         MARCH        |" << endl;
	cout << "| SU MO TU WE TH FR SA | SU MO TU WE TH FR SA | SU MO TU WE TH FR SA |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "+----------------------+----------------------+----------------------+" << endl;
	cout << "|        APRIL         |          MAY         |         JUNE         |" << endl;
	cout << "| SU MO TU WE TH FR SA | SU MO TU WE TH FR SA | SU MO TU WE TH FR SA |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "+----------------------+----------------------+----------------------+" << endl;
	cout << "|         JULY         |        AUGUST        |       SEPTEMBER      |" << endl;
	cout << "| SU MO TU WE TH FR SA | SU MO TU WE TH FR SA | SU MO TU WE TH FR SA |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "+----------------------+----------------------+----------------------+" << endl;
	cout << "|        OCTOBER       |       NOVEMBER       |       DECEMBER       |" << endl;
	cout << "| SU MO TU WE TH FR SA | SU MO TU WE TH FR SA | SU MO TU WE TH FR SA |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "|                      |                      |                      |" << endl;
	cout << "+----------------------+----------------------+----------------------+" << endl;
    }

    int firstdays[12], year;
    bool isleap;
};

int main( int argc, char* argv[] )
{
    int y;
    calender cal;

    while( true )
    {
	system( "cls" );
	cout << "Enter the year( yyyy ) --- ( 0 to quit ): "; 
	cin >> y;
	if( !y ) return 0;

	cal.drawCalender( y );
	cout << endl << endl << endl << endl << endl << endl << endl << endl;

	system( "pause" );
    }
    return 0;
}