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Week numbers according to ISO8601

By , 7 Mar 2010
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The code snippet below returns the first Thursday of a given year without iterating anything.
DateTime FirstThursday(int year) {
	DateTime dt=new DateTime(year, 1, 1);
	return dt.AddDays((11-(int)dt.DayOfWeek)%7);
The formula used may seem a bit bizarre, it computes the distance between first of January and first Thursday of January, where DayOfWeek.Thursday=4, and another week is added to avoid negative numbers; and eventually a modulo 7 operation fixes everything.
More such stuff can be found here[^].
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About the Author

Luc Pattyn
Software Developer (Senior) Perceler
Belgium Belgium
I am an engineer with a background in electronics, software and mathematics.
I develop technical software, both for embedded systems and for desktop equipment. This includes operating systems, communication software, local networks, image processing, machine control, automation, etc.
I have been using all kinds of microcontrollers and microprocessors (Intel 4004/8080/8051/80386/Pentium, Motorola 680x/680x0/ColdFire/PowerPC, Microchip PIC, Altera NIOS, and many more), lots of programming languages (all relevant assemblers, Fortran, Basic, C, Java, C#, and many more), and different operating systems (both proprietary and commercial).
For desktop applications and general development tools I have been using both UNIX systems and Mac/MacOS for many years, but I have switched to x86-based PCs with Windows, Visual Studio and the .NET Framework several years ago.
I specialize in:
- cross-platform development (making software that runs on diverse hardware/OS combinations)
- instruction set simulation
- improving software performance, i.e. making sure the software runs the job at hand in as short a time as possible on the given hardware. This entails algorithm selection, implementation design, accurate measurements, code optimisation, and sometimes implementing virtual machines, applying SIMD technology (such as MMX/SSE), and more.

Comments and Discussions

GeneralNice Dear PinmemberThatsAlok10-Aug-10 0:31 
GeneralReason for my vote of 5 very useful Pinmemberjohannesnestler3-Aug-10 21:59 
Reason for my vote of 5
very useful

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