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#: using System;
using System.Collections.Generic; 
using System.Linq;
using System.Text;

namespace CalendarStuff
{
 
    class Program
    {
        static void Main(string[] args)
        {
            Console.WindowHeight = 46;
            Console.Write(buildMonths(new DateTime(1969, 1, 1)));
            Console.Read(); 
        }
        private static string buildMonths(DateTime date)
        {
            StringBuilder sb = new StringBuilder();
            sb.AppendLine(center("[Snoop]", 24 * 3));
            sb.AppendLine();
            sb.AppendLine(center(date.Year.ToString(), 24 * 3));

            List<DateTime> dts = new List<DateTime>();
            while (true)
            {
                dts.Add(date);
                if (date.Year != ((date = date.AddMonths(1)).Year))
                {
                    break;
                }
            }
            var jd = dts.Select(a => buildMonth(a).GetEnumerator()).ToArray();
            
            int sCur=0;
            while (sCur<dts.Count)
            {
                sb.AppendLine();
                int curMonth=0; 
                var j = jd.Where(a => curMonth++ >= sCur && curMonth - 1 < sCur + 3).ToArray(); 
                sCur += j.Length; 
                bool breakOut = false;
                while (!breakOut)
                {
                    int inj = 1;
                    foreach (var cd in j)
                    {
                        if (cd.MoveNext())
                        {
                            sb.Append((cd.Current.Length == 21 ? cd.Current : cd.Current.PadRight(21, ' ')) + "     ");
                        }
                        else
                        {
                            sb.Append("".PadRight(21, ' ') + "     ");
                            breakOut = true;
                        }
                        if (inj++ % 3 == 0) sb.AppendLine();
                    }
                }

            }
            return sb.ToString();
        }


        private static IEnumerable<string> buildMonth(DateTime date)
        {
            yield return center(date.ToString("MMMM"),7*3);
            var j = DateTime.DaysInMonth(date.Year, date.Month);
            yield return Enum.GetNames(typeof(DayOfWeek)).Aggregate("", (current, result) => current + (result.Substring(0, 2).ToUpper() + " "));
            string cur = "";
            int total = 0;

            foreach (var day in Enumerable.Range(-((int)date.DayOfWeek),j + (int)date.DayOfWeek))
            {
                cur += (day < 0 ? "  " : ((day < 9 ? " " : "") + (day + 1))) +" ";
                if (total++ > 0 && (total ) % 7 == 0)
                {
                    yield return cur;
                    cur = "";
                }
            }
            yield return cur;
        }
        private static string center(string s, int len)
        {
            return (s.PadLeft((len - s.Length) / 2 + s.Length, ' ').PadRight((len), ' '));
        } 
    }
}