More elegant way to get "Friday of last week"?

[sherifffruitfly]

Hi all,

This is how I'm currently getting Friday of last week. It strikes me as
cumbersome. Is there a slicker/more elegant way?

Thanks for any ideas,

cdj

private string prevFridayStrin g(DateTime day)
{
DateTime rv;
int offset = 0;

switch (day.DayOfWeek)
{
case DayOfWeek.Sunda y:
offset = 5;
break;
case DayOfWeek.Monda y:
offset = 4;
break;
case DayOfWeek.Tuesd ay:
offset = 3;
break;
case DayOfWeek.Wedne sday:
offset = 2;
break;
case DayOfWeek.Thurs day:
offset = 1;
break;
case DayOfWeek.Frida y:
offset = 0;
break;
case DayOfWeek.Satur day:
offset = -1;
break;
}

rv = day.AddDays(-7 + offset);
return rv.ToShortDateS tring();
}

[Arne Vajhøj]

sherifffruitfly wrote:

This is how I'm currently getting Friday of last week. It strikes me as
cumbersome. Is there a slicker/more elegant way?

Something like:

DateTime dt = DateTime.Now;
while(dt.DayOfW eek != DayOfWeek.frida y) dt = dt.AddDays(-1);

[untested - please check]

Arne

[sherifffruitfly]

Arne Vajhøj wrote:

>
DateTime dt = DateTime.Now;
while(dt.DayOfW eek != DayOfWeek.frida y) dt = dt.AddDays(-1);

Nice. The idea is perfectly clear - thanks!

cdj

[Arne Vajhøj]

sherifffruitfly wrote:

Arne Vajhøj wrote:

>DateTime dt = DateTime.Now;
while(dt.DayOf Week != DayOfWeek.frida y) dt = dt.AddDays(-1);

Nice. The idea is perfectly clear - thanks!

If you want to go 7 days back if today is Friday then you will need:

DateTime dt = DateTime.Now.Ad dDays(-1);

You should also note that it is not optimized for speed.

But any maintenance programmer reading the code will understand
the "algorithm" .

Arne

[nick.fletcher]

You can achieve this quite easily using recurssion

public partial class Form1 : Form
{

private DateTime lastFriday;

public Form1()
{
InitializeCompo nent();
}

private void monthCalendar1_ DateSelected(ob ject sender,
DateRangeEventA rgs e)
{
selectedText.Te xt = e.Start.ToShort DateString();
GetLastFriday(e .Start);
lastFridayText. Text = lastFriday.ToSh ortDateString() ;
}

private void GetLastFriday(D ateTime dateTime)
{
dateTime = dateTime.Subtra ct(new TimeSpan(1,0,0, 0));
if (dateTime.DayOf Week == DayOfWeek.Frida y)
{
lastFriday = dateTime;
return;
}
else
GetLastFriday(d ateTime);
}
}

Remember to add a check so your method doesnt execute more than 7 times
(days in a week) or you could get a stack overflow if things go wrong

On Nov 16, 1:14 pm, "sherifffruitfl y" <sherifffruit.. [e-mail]>
wrote:

Hi all,

This is how I'm currently getting Friday of last week. It strikes me as
cumbersome. Is there a slicker/more elegant way?

Thanks for any ideas,

cdj

private string prevFridayStrin g(DateTime day)
{
DateTime rv;
int offset = 0;

switch (day.DayOfWeek)
{
case DayOfWeek.Sunda y:
offset = 5;
break;
case DayOfWeek.Monda y:
offset = 4;
break;
case DayOfWeek.Tuesd ay:
offset = 3;
break;
case DayOfWeek.Wedne sday:
offset = 2;
break;
case DayOfWeek.Thurs day:
offset = 1;
break;
case DayOfWeek.Frida y:
offset = 0;
break;
case DayOfWeek.Satur day:
offset = -1;
break;
}

rv = day.AddDays(-7 + offset);
return rv.ToShortDateS tring();
}

[Peter Duniho]

<ni***********@ iinet.net.auwro te in message
news:11******** **************@ h54g2000cwb.goo glegroups.com.. .

You can achieve this quite easily using recurssion

Yes, you can. And it's a classic example of a problem that *shouldn't* be
done using recursion.

Don't use recursion when a simple loop will suffice. Recursion is great if
you have a need to unwind all of your state. It's a complete waste of
coding effort, stack space, and execution time when one never needs to
actually revisit previous results, as is the case here.

Pete

[Stephany Young]

Did everyone miss?:

private string prevFridayStrin g(DateTime day)
{
return day.AddDays(-((int)day.DayOf Week) + 2)).ToShortDate String();
}

Remember that the underlying values for the DayOfWeek enumeration are int's
with Sunday being 0 and Saturday being 6.

Therfore is is simply a matter of subtracting the value of (day.DayOfWeek
plus 2).
"sherifffruitfl y" <sh************ *@gmail.comwrot e in message
news:11******** *************@e 3g2000cwe.googl egroups.com...

Hi all,

This is how I'm currently getting Friday of last week. It strikes me as
cumbersome. Is there a slicker/more elegant way?

Thanks for any ideas,

cdj

private string prevFridayStrin g(DateTime day)
{
DateTime rv;
int offset = 0;

switch (day.DayOfWeek)
{
case DayOfWeek.Sunda y:
offset = 5;
break;
case DayOfWeek.Monda y:
offset = 4;
break;
case DayOfWeek.Tuesd ay:
offset = 3;
break;
case DayOfWeek.Wedne sday:
offset = 2;
break;
case DayOfWeek.Thurs day:
offset = 1;
break;
case DayOfWeek.Frida y:
offset = 0;
break;
case DayOfWeek.Satur day:
offset = -1;
break;
}

rv = day.AddDays(-7 + offset);
return rv.ToShortDateS tring();
}

[PS]

<ni***********@ iinet.net.auwro te in message
news:11******** **************@ h54g2000cwb.goo glegroups.com.. .

You can achieve this quite easily using recurssion

public partial class Form1 : Form
{

private DateTime lastFriday;

public Form1()
{
InitializeCompo nent();
}

private void monthCalendar1_ DateSelected(ob ject sender,
DateRangeEventA rgs e)
{
selectedText.Te xt = e.Start.ToShort DateString();
GetLastFriday(e .Start);
lastFridayText. Text = lastFriday.ToSh ortDateString() ;
}

private void GetLastFriday(D ateTime dateTime)
{
dateTime = dateTime.Subtra ct(new TimeSpan(1,0,0, 0));
if (dateTime.DayOf Week == DayOfWeek.Frida y)
{
lastFriday = dateTime;
return;
}
else
GetLastFriday(d ateTime);
}
}

Remember to add a check so your method doesnt execute more than 7 times
(days in a week) or you could get a stack overflow if things go wrong

Not only is it unnecessarily complex it is also incorrect. If you started
with Saturday it would return the Friday from the same week not "Friday Of
Last Week".

PS

>
On Nov 16, 1:14 pm, "sherifffruitfl y" <sherifffruit.. [e-mail]>
wrote:

>Hi all,

This is how I'm currently getting Friday of last week. It strikes me as
cumbersome. Is there a slicker/more elegant way?

Thanks for any ideas,

cdj

private string prevFridayStrin g(DateTime day)
{
DateTime rv;
int offset = 0;

switch (day.DayOfWeek)
{
case DayOfWeek.Sunda y:
offset = 5;
break;
case DayOfWeek.Monda y:
offset = 4;
break;
case DayOfWeek.Tuesd ay:
offset = 3;
break;
case DayOfWeek.Wedne sday:
offset = 2;
break;
case DayOfWeek.Thurs day:
offset = 1;
break;
case DayOfWeek.Frida y:
offset = 0;
break;
case DayOfWeek.Satur day:
offset = -1;
break;
}

rv = day.AddDays(-7 + offset);
return rv.ToShortDateS tring();
}

[Jeff Louie]

Just for fun, here is the actual algorithm in C++ based on Zeller and
yes 0 for Sunday is how it was done:

GetFirstDayInMo nth
// Days since Sunday 0-6
// Based on Zeller
// ASSERT Year>1, Month>=1 && <=12.
int CCalendar::GetF irstDayInMonth( unsigned int Year, unsigned int Month)
{
const int day=1;
if (Month < 3) {
Month +=12;
Year -= 1;
}
return
((day+1+(Month* 2)+(int)((Month +1)*3/5)+Year+(int)(Y ear/4)-(int)(Year/100
)+(int)(Year/400))%7);
}

Regards,
Jeff

*** Sent via Developersdex http://www.developersdex.com ***

[sherifffruitfly]

Jeff Louie wrote:

Just for fun, here is the actual algorithm in C++ based on Zeller and
yes 0 for Sunday is how it was done:

Wow - this turned into a whole lot more "fun" than I was expecting! I
especially love the recursive solution - lolol!