how calculate the number of days between two date ?

[jyb]

hi all
i need for my project ,to know the method how calculate how many days and hours between two date ,for example between today and 01/01/2013 (january/01/2013)
somebody could help me? what i need is a mathematical method applicable to a pic
i use a picaxe 40x2 (pic 18f45k22)
i built a display panel of eight led 8x8 dot matrix blocks .this system display shifting texts and time ( i use for this a ds1307 rtc) all is running correctly and i am locked only by this question!!

thanks
jyb

 

[eclectic]

Here's a thread to start off:
http://www.picaxeforum.co.uk/showthread.php?8674-Julian-date-code-for-picaxe&highlight=julian

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[Dippy]

Google "algorithm for days between dates" and you will find a lot of good ones.

 

[jyb]

thanks a lot for your instant answer
it is exactly what i need

 

[hippy]

Don't forget to take into account Daylight Saving Time when calculating between two dates if you want accurate time periods.

Every millennium countdown clock I saw was an hour out ( or a year and an hour out to be pedantic ) and had to be adjusted when BST ended - which is tonight in Europe in case anyone's forgotten the clocks go back.