Calender

[gobinath]

Is it possible to program for an calender? if it is possible,give me an idea.

[ravenspoint]

Date calculations are notoriously difficult, with many frustrating special cases that will catch you if you do not test your code to death with every possible date.

Do not undertake this lightly!

That said, a good place to start is

	__time64_t long_time;
        struct tm myTime

	_time64( &long_time );                /* Get time as long integer. */
	myTime = *_localtime64( &long_time ); /* Convert to local time. */

[weaknessforcats]

Presumably, you would have 12 months where months were 28,29,30 or 31 days based on the year.

Can you see that a year is a container of months and a month is a container of days?

Try to write something on paper before attempting to code.

[ravenspoint]

Presumably, you would have 12 months where months were 28,29,30 or 31 days based on the year.

Can you see that a year is a container of months and a month is a container of days?

Try to write something on paper before attempting to code.

Gosh, weaknessforcats , you are so very modern with your containers of containers! Then you spoil it all by calling for paper and pencil!

Who contains the years, I wonder? And how does poor old febuary know whether it is in a leap year or not?

I have found that it is better to create the days, one at a time, as they are needed - just like real life, really. The "struct tm" is a handy little thing for keeping track of all the pesky details.

[TRScheel]

Gosh, weaknessforcats , you are so very modern with your containers of containers! Then you spoil it all by calling for paper and pencil!

Who contains the years, I wonder? And how does poor old febuary know whether it is in a leap year or not?

I have found that it is better to create the days, one at a time, as they are needed - just like real life, really. The "struct tm" is a handy little thing for keeping track of all the pesky details.

if (year % 4) == 0
nextday = feb 29
else
nextday = mar 1

[ravenspoint]

if (year % 4) == 0
nextday = feb 29
else
nextday = mar 1

Yes, this works if the month knows what year it is contained by. Which is why I asked about just that.

[weaknessforcats]

Gosh, weaknessforcats , you are so very modern with your containers of containers! Then you spoil it all by calling for paper and pencil!

Who contains the years, I wonder? And how does poor old febuary know whether it is in a leap year or not?

Yes, indeed. Who does contain the years? Are there years?? What kind calendar it is it?? Gregorian? Tibetan? Astronomical? Julian?

You need to desgin before coding. That iswhy things like UML are in existence in the first place.

A struct tm may not work in a particular application or operating system.

[ravenspoint]

A struct tm may not work in a particular application or operating system.

Really? As I understand it, it is part of the C run time library. I believe that a compliant C compiler toolset should provide it.

[weaknessforcats]

It is not required that C be supported by C++. In several areas C code just doesn't compile in C++.

[Darryl]

if (year % 4) == 0
nextday = feb 29
else
nextday = mar 1

What's the day after Febuary 28, 1900?

[TRScheel]

What's the day after Febuary 28, 1900?

Throw in % 100 to check those years. Or make a method that returns leap year or not.

So that would be something like

[code=cpp]
bool LeapYear()
{
return currentYear % 4 == 0 && currentYear % 100 != 0;
}
[/code]

Make that accessible to the months, particularly February, and February checks that before going to the 29th. If all months inherit a base, you could override the next day function on February to just check that, while every other month is oblivious to the leap year. Sadly, this is a model where the month does have to be aware of what year it is in.

[weaknessforcats]

I think the leap year check is that the leap year is divisible by 4 and not by 400.

1600 and 2000 were not leap years.

If your calendar doesn't need to go out that far, the 400 check isn't worth it.

[JosAH]

For the Gregorian calendar, Zeller's congruence method comes in extremely
handy; google for it.

kind regards,

Jos

[weaknessforcats]

Zeller's congruence

What is that!! I have seen you pull all sorts of rabbits like this out of your hat.

Where did you learn all of this stuff? :)

[weaknessforcats]

2,620 hits on Google for Zeller's Congruence.

What else have I failed to learn?