Calender Program In C#

Beginning of Calendar.cs

 This program prints out the calendar for a full year, specified by the user.

using System;

class Calendar

{

const int Sunday    = 0;

const int Monday    = 1;

const int Tuesday   = 2;

const int Wednesday = 3;

const int Thursday  = 4;

const int Friday    = 5;

const int Saturday  = 6;

static void Main (string[] args)

{

    int year;

    GiveInstructions();

    year = GetYearFromUser();

    PrintCalendar(year);

}

static void GiveInstructions ()

{

    Console.WriteLine("This program displays a calendar for a full");

    Console.WriteLine("year.  The year must not be before 1900.");

}

static int GetYearFromUser ()

{

    int year = 1900;

    while (true)

    {

        Console.Write("Which year? ");

        year = Int32.Parse(Console.ReadLine());

        if (year >= 1900) return year;

        Console.WriteLine("The year must be at least 1900.");

    };

}

static void PrintCalendar(int year)

{

    int month;

    for (month = 1; month <= 12; month++) 

    {

        PrintCalendarMonth(month, year);

        Console.WriteLine();

    }

}

static void PrintCalendarMonth(int month, int year)

{

    int weekday, nDays, day;

    Console.WriteLine("    " + (MonthName(month)) + " " + year);

    Console.WriteLine(" Su Mo Tu We Th Fr Sa");

    nDays = MonthDays(month, year);

    weekday = FirstDayOfMonth(month, year);

    IndentFirstLine(weekday);

    for (day = 1; day <= nDays; day++)

    {

       if (day > 9) Console.Write(" " + day);

       else Console.Write("  " + day);

       if (weekday == Saturday) Console.WriteLine();

       weekday = (weekday + 1) % 7;

    }

    if (weekday != Sunday) Console.WriteLine();

}

static void IndentFirstLine(int weekday) 

{

    int i;

    for (i = 0; i < weekday; i++) 

    {

        Console.Write("   ");

    }

}      

static int MonthDays(int month, int year)

 {

    switch (month) 

    {

      case 2:

        if (IsLeapYear(year)) return (29);

        return (28);

      case 4: case 6: case 9: case 11:

        return (30);

      default:

        return (31);

    }

}

static int FirstDayOfMonth(int month, int year)

{

    int weekday, i;

    weekday = Monday;

    for (i = 1900; i < year; i++) 

    {

        weekday = (weekday + 365) % 7;

        if (IsLeapYear(i)) weekday = (weekday + 1) % 7;

    }

    for (i = 1; i < month; i++)

    {

        weekday = (weekday + MonthDays(i, year)) % 7;

    }

    return (weekday);

}

static string MonthName(int month)

{

    switch (month)

   {

      case  1: return ("January");

      case  2: return ("February");

      case  3: return ("March");

      case  4: return ("April");

      case  5: return ("May");

      case  6: return ("June");

      case  7: return ("July");

      case  8: return ("August");

      case  9: return ("September");

      case 10: return ("October");

      case 11: return ("November");

      case 12: return ("December");

      default: return ("Illegal month");

    }

}

static bool IsLeapYear(int year)

{

    return ( ((year % 4 == 0) && (year % 100 != 0))

             || (year % 400 == 0) );

} 

}