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C/C++

 
Calendars are integral part of our lives. All of us need to remember dates of scheduled meetings, girlfriend's birth day and of course for schedules of coding, debugging and testing. Being a developer it always interests me to develop my own piece of code to generate a calendar, capable of displaying months-years-date-day etc. (that too in the pretty format) for next few thousand years. Well, it is not a very very big mathematics. One golden rule is all you need to know and you are done. I developed this calendar application in the year 2002 (under C), which you can easily translate to C++ or any language you love to work in.

I have used legacy C compiler (Turbo) but you may compile the same on GCC (hopefully) correctly. The application uses Up, Down, Left and Right arrow keys for navigation of months and years. If you really want to see the EXE in execution before understanding the code (or copying it) click here (13.6 KB) to download it off my site.

And the golden rule is: 01-Jan-1900 was Monday and a leap year has of 29 days in February. I have used the default months and years (y and m variables) as 11 and 1979 respectively, because they are from my birth-date. If you wish, you may use command line arguments and/or different months and years too.

Here is the source code:
/* Displaying calendar in a table prepared in the text mode */

#include <stdio.h>
#include <conio.h>
#include <dos.h>

enum boolean {false, true};

enum boolean isLeap(int year)
{
if ((year % 4) == 0 && (year % 100 != 0) || (year % 400) == 0)
	return true;	/* the year is a leap year */
else
	return false;	/* the year is not a leap year */
}

getkey()
{
union REGS i,o;

while (!kbhit())
	;
i.h.ah = 0;
int86(22, &i, &o);
return(o.h.ah);	  /* returns the scan code of the key that has been hit */
}

main()
{
int year_arr[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
int leap_year_arr[12] = {31,29,31,30,31,30,31,31,30,31,30,31};
char month[12][10] = {"January","February","March","April","May","June",
	"July","August","September","October","November","December"};
long days;	/* the days holder */
int y, m;	/* the year and month holder */
int y1, i, nod;	/* nod holds the number of days in current month */
int res, lc, code;
char ch, k;

y = 1979;
m = 11;

do
{
	clrscr();
	y1 = y;
	days = 0;

	while ((y - 1) >= 1900)
	{
		if (isLeap(y - 1) == true)
			for (i = 0; i < 12; i++)
				days += leap_year_arr[i];
		else
			for (i = 0; i < 12; i++)
				days += year_arr[i];
		y--;
	}

	for (i = 0; i < (m - 1); i++)
	{
		if (isLeap(y1) == true)
			days += leap_year_arr[i];
		else
			days += year_arr[i];
	}

	if (isLeap(y1) == true)
		nod = leap_year_arr[m - 1];
	else
		nod = year_arr[m - 1];

	res = days % 7;
	i = 1;

	/* drawing table border - start */

	ch = 218;
	printf("%c", ch);
	ch = 196;
	for (k = 1; k < 37; k++)
		printf("%c", ch);
	ch = 191;
	printf("%c", ch);
	ch = 179;
	printf("\n%c", ch);

	printf("     %10s %d Calendar", month[m-1], y1);
	printf("%8c", ch);

	ch = 195;
	printf("\n%c", ch);

	ch = 196;
	for (k = 1; k < 37; k++)
		printf("%c", ch);

	ch = 180;
	printf("%c", ch);

	ch = 179;
	printf("\n%c", ch);

	printf("  Mon  Tue  Wed  Thu  Fri  Sat  Sun");

	printf("%2c", ch);

	ch = 195;
	printf("\n%c", ch);

	ch = 196;
	for (k = 1; k < 37; k++)
		printf("%c", ch);

	ch = 180;
	printf("%c", ch);

	ch = 179;
	printf("\n%c", ch);

	lc = 1;

	switch(res)
	{
		case 1:
			printf("     ");
			lc += 1;
			break;
		case 2:
			printf("          ");
			lc += 2;
			break;
		case 3:
			printf("               ");
			lc += 3;
			break;
		case 4:
			printf("                    ");
			lc += 4;
			break;
		case 5:
			printf("                         ");
			lc += 5;
			break;
		case 6:
			printf("                              ");
			lc += 6;
			break;
	}

	while (i <= nod)
	{
		printf("%5d", i);
		lc++;
		if (lc == 8)
		{
			printf("%2c\n", ch);
			lc = 1;
		}
		if (lc == 1)
			printf("%c", ch);
		i++;
	}

	for (; lc < 8; lc++)
		printf("     ");
	printf("%2c", ch);

	ch = 192;
	printf("\n%c", ch);

	ch = 196;
	for (k = 1; k < 37; k++)
		printf("%c", ch);

	ch = 217;
	printf("%c", ch);

	printf("\n\nCode (c) 2002. Krishna Kumar Khatri.");
	printf("\nPress <Esc> to exit...");
	code = getkey();

	if (code == 72)         /* up arrow key -- previous year */
	{
		if (y1 == 1900)
			y = 9999;
		else
			y = y1 - 1;
	}
	else if (code == 80)	/* down arrow key -- next year */
	{
		if (y1 == 9999)
			y = 1900;
		else
			y = y1 + 1;
	}
	else if (code == 75)	/* left arrow key -- previous month */
	{
		if (m == 1)
			m = 12;
		else
			m -= 1;
		y = y1;
	}
	else if (code == 77)	/* right arrow key -- next month */
	{
		if (m == 12)
			m = 1;
		else
			m += 1;
		y = y1;
	}
	else
		break;

} while (1);
}


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