N° of the week from a date

[Dieter]

(11-04-2015 07:54 AM)ggauny@live.fr Wrote:  Thanks for encouragements ! I know that if the 01/01/yyyy biguin a thursday (jeudi), the n° of week is 1, if there is less than 4 days in the biguining year, the week is noted "0". Then at the end of the year we, sometimes, have a "53" week, wich is combinated with the following first week of the following YEAR+1.

Sorry, but there is no week 0. Weeks have numbers between 1 and 53. The rule is quite simple: If a week falls both into the old and the new year, it counts either as the last week (52 or 53) of the old year or week 1 of the new year – depending on which year has more days of that week.

This is also shown in your calendar examples. There really is no week 0. ;-)

(11-04-2015 07:54 AM)ggauny@live.fr Wrote:  The last week of 2015 has 4 days (28,29,30,31 : monday, thuesday, wednessday and thursday) is noted of course n°53.

Right. It has at least four days in it, i.e. the major part of a week.

(11-04-2015 07:54 AM)ggauny@live.fr Wrote:  On the other hand, in 2016 there will be only 3 days on biguining year (Friday 1, saturday 2 and sunday 3) so the first week of 2016 will be of course noted, officialy on french calendar, n° 0.

There is no week 0. At least the ISO standard does not know of such a week number. This week (monday through sunday) still is week 53 of 2015. That week starts in 2015 and ends in 2016. Yes, the three first days of january 2016 count as week 53 of 2015.

(11-04-2015 07:54 AM)ggauny@live.fr Wrote:  I've attempted to put photos of the calendar, but too bigs for our forum.

The screenshots also show no week 0. Just week 53/2015 (beginning in 2015 and ending in 2016) and week 1/2016 (starting on 4 January).

Once again: the ISO rule really is very simple. If the major part of a week falls into the previous year, that's the last week (52 or 53) of that year. If the major part falls into the new year, that's its week 1.

Dieter