Calculate the date of fifth tuesday of the month?

Any suggestions how to calculate fifth tuestay of the month...
There is of course several  methods, but what is the simplest way?
Who is Participating?

Commented:
Fixed:
``````function FindDate(Dt:TDate;Dy,Num:Integer):TDate;
var
i,j:integer;
ddte:TDate;
begin
Result := EncodeDate(1700,1,1);
j:=0;
for i:= 1 to DaysInAMonth(YearOf(dt),MonthOf(dt)) do
begin
ddte := EncodeDate(YearOf(dt),MonthOf(dt),i);
if DayOfWeek(ddte) = Dy then
begin
inc(j);
if j = Num then
begin
Result := ddte;
exit;
end;
end;
end;
if J < Num then
Result := EncodeDate(1700,1,1);
end;

procedure TForm1.Button2Click(Sender: TObject);
var
Dt:TDate;
begin
Dt := FindDate(now,3,5);
If Dt = EncodeDate(1700,1,1) then
Showmessage('There is no date for that number in this month')
else
Showmessage(Datetostr(Dt));
end;
``````
0

Commented:
try
``````function FifthTuesday(ADate: TDateTime): TDateTime;
var
Lastday: TDateTime;
DOW: Word;
begin
Result := 0;
DOW := DayOfTheWeek(Lastday);
if WeekOfTheMonth(LastDay) = 5 then
begin
if DOW = 2 then
Result := LastDay
else if DOW > 2 then
begin
while DOW > 2 do
begin
LastDay := IncDay(LastDay, -1);
DOW := DayOfTheWeek(Lastday);
end;
Result := LastDay;
end;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(DatetimetoStr(FifthTuesday(Date))) //for this month
end;
``````
0

Commented:
Here is a function to get the date of and day as per any specified number:
``````function FindDate(Dt:TDate;Dy:String;Num:Integer):TDate;
var
i,j:integer;
ddte:TDate;
Dte : String;
begin
j:=0;
for i:= 1 to DaysInMonth(MonthOf(dt)) do
begin
ddte := EncodeDate(YearOf(dt),MonthOf(dt),i);
Dte := FormatDateTime('ddd',ddte);
if Dte = Dy then
begin
inc(j);
if j = Num then
begin
Result := ddte;
exit;
end;
end;
end;
if J < Num then
Result := StrToDate('01/01/1700');
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
If Datetostr(FindDate(now,'Tue',5)) = StrToDate('01/01/1700') then
Showmessage('There is no date for that number in this month')
else
Showmessage(DateToStr(Datetostr(FindDate(now,'Tue',5))));
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
ShortDateFormat := 'dd/mm/yyyy';
end;
``````

It can be improved more, this is to show the idea only.
0

Commented:
@ejla51

What do you need to do if there is NO fifth Tuesday in the month?
0

Commented:
small fix in my code:
``````function FindDate(Dt:TDate;Dy:String;Num:Integer):TDate;
var
i,j:integer;
ddte:TDate;
Dte : String;
begin
Result := StrToDate('01/01/1700');
j:=0;
for i:= 1 to DaysInMonth(MonthOf(dt)) do
begin
ddte := EncodeDate(YearOf(dt),MonthOf(dt),i);
Dte := FormatDateTime('ddd',ddte);
if Dte = Dy then
begin
inc(j);
if j = Num then
begin
Result := ddte;
exit;
end;
end;
end;
if J < Num then
Result := StrToDate('01/01/1700');
end;

procedure TForm1.Button2Click(Sender: TObject);
var
Dt:TDate;
begin
Dt := FindDate(now,'Tue',5);  // or FindDate(now,'Thu',5);
If Dt = StrToDate('01/01/1700') then
Showmessage('There is no date for that number in this month')
else
Showmessage(Datetostr(Dt));
end;
``````
0

Author Commented:
Hi fellows,
Have tested both without succes... I think partly due to national settings (short daynames?/FormatDateTime?)...

ewangoya... please notice that only 5th tuesaday is intrested, not last if there is only 4  tuesdays in the month.

jimyX: My testresult- if there is 5 tuesdays in the month, date was not found, if only 4 tuesdays "Invalid argument to date encode"

aikimark: Usage "Custom calendar" - eg. get dates to  TStringList (5th tuesday dates only) when year is selected with the SpinEdit!
0

Commented:
Can you show the date that you tested this function with please? and also did you set the short date format?
0

Commented:

First you need to check how if the first day of the week is Monday or Sunday in your LOCALE
If Sunday, then DOW should be 3
Modify my function to
``````function FifthTuesday(ADate: TDateTime): TDateTime;
var
Lastday: TDateTime;
DOW: Word;
begin
Result := 0;
DOW := DayOfTheWeek(Lastday);
if WeekOfTheMonth(LastDay) = 5 then
begin
if DOW = 2 then
Result := LastDay
else if DOW > 2 then
begin
while (WeekOfTheMonth(LastDay) = 5) and (DOW > 2) do
begin
LastDay := IncDay(LastDay, -1);
DOW := DayOfTheWeek(Lastday);
end;
if DOW = 2 then
Result := LastDay;
end;
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(DatetimetoStr(FifthTuesday(Date))) //for this month
end;
``````
0

Commented:
Forget the LOCALE, in Delphi way Monday is always 1 so Tuesday is 2.
My function here should work properly with the extra check

var
Lastday: TDateTime;
DOW: Word;
begin
Result := 0;
DOW := DayOfTheWeek(Lastday);
if WeekOfTheMonth(LastDay) = 5 then
begin
if DOW = 2 then
Result := LastDay
else if DOW > 2 then
begin
while (WeekOfTheMonth(LastDay) = 5) and (DOW > 2) do
begin
LastDay := IncDay(LastDay, -1);
DOW := DayOfTheWeek(Lastday);
end;
if DOW = 2 then
Result := LastDay;
end;
end;
end;
0

Author Commented:
ewangoya:
I'm using Swedish National settings.
ShortDate 2011-03-23
--
procedure TForm1.Button1Click(Sender: TObject);
begin
ShowMessage(DateToStr(FifthTuesday(MonthCalendar1.Date)));
end;

testresults for year 2011:
Mars -> 2011-03-29 Correct!
May  ->  1899-12-30 but would be 2011-05-31
June -> 2011-06-28  This is 4th tuesday
Aug -> 1899-12-30 but would be 2011-08-30
Sept -> 2011-09-27 This 4th tuesday
Nov ->1899-12-30  but would be  2011-11-29
Dec  -> 2011-12-27 is 4th tuesday

0

Author Commented:
@jimyX:
My computer don't allow to set "ShortDateFormat  := 'dd/mm/yyyy'

My XP uses Swedish settings yyy-mm-dd

0

Commented:
Here is an updated one, can you check it please:
``````function FindDate(Dt:TDate;Dy,Num:Integer):TDate;
var
i,j:integer;
ddte:TDate;
Dte : String;
begin
Result := EncodeDate(1700,1,1);
j:=0;
for i:= 1 to DaysInMonth(MonthOf(dt)) do
begin
ddte := EncodeDate(YearOf(dt),MonthOf(dt),i);
if DayOfWeek(ddte) = Dy then
begin
inc(j);
if j = Num then
begin
Result := ddte;
exit;
end;
end;
end;
if J < Num then
Result := EncodeDate(1700,1,1);
end;

procedure TForm1.Button2Click(Sender: TObject);
var
Dt:TDate;
begin
Dt := FindDate(now,3,5);
If Dt = EncodeDate(1700,1,1) then
Showmessage('There is no date for that number in this month')
else
Showmessage(Datetostr(Dt));
end;
``````
0

Author Commented:
@jimyX:
you are very close now :)
Error occured (Invalid argument to date encode) IF there is only 4 tuesdays AND less than 31 days in the month!
All 5th tuesdays are found. Correct result  handling on 31 days months with 4 tuesdays.
0

Commented:
@ejla51

So you want to pass a year value to a function and get all the 5th Tuesday dates in that year?
0

Author Commented:
@aikimark:
Yes... something like

for Month := 1 to 12 do
if FifthTuesday(Year,Month) <> nil then
0

Commented:

Interesting, I just found a bug in Delphi

When in May, this function is returning 06/01/2011

So the whole function breaks, this is bad, I'll try and get a workaround
0

Commented:
@ ejla51
Any comment on my last code?

@ ewangoya
It works fine in Delphi 7 and 2009. I tried this way:
``````procedure TForm1.Button1Click(Sender: TObject);
begin
showmessage(DatetoStr(EndOfTheMonth(EncodeDate(2011,5,3))));
end;
``````
0

Commented:

Weird stuff, I'm using Delphi 2010
0

Commented:

My Delphi is behaving really weird, Anyway I tested this with all the months
``````function FifthTuesday(ADate: TDateTime): TDateTime;
var
CheckDay: TDateTime;
Index: Integer;
WorkMonth: Word;
DD, MM, YY: WORD;
begin
Result := 0;
CheckDay := EncodeDate(YY, MM, 1);

//start by getting first tuesday
while DayOfTheWeek(CheckDay) <> 2 do
CheckDay := IncDay(CheckDay, 1);

//now we have first tuesday
WorkMonth := MM;
Index := 1;
while (WorkMonth = MM) and (Index < 5) do
begin
CheckDay := IncDay(CheckDay, 7);
WorkMonth := MonthOf(CheckDay);
Inc(Index);
end;
if (WorkMonth = MM) and (Index = 5) then
Result := CheckDay
else
Result := 0;
end;

procedure TForm3.Button1Click(Sender: TObject);
begin
ShowMessage(DateToStr(FifthTuesday(MonthCalendar1.Date)));
end;
``````
0

Commented:
Or just pass Month and Year

``````function FifthTuesday1(MM, YY: Integer): TDateTime;
var
CheckDay: TDateTime;
Index: Integer;
WorkMonth: Word;
begin
Result := 0;
CheckDay := EncodeDate(YY, MM, 1);

//start by getting first tuesday
while DayOfTheWeek(CheckDay) <> 2 do
CheckDay := IncDay(CheckDay, 1);

//now we have first tuesday
WorkMonth := MM;
Index := 1;
while (WorkMonth = MM) and (Index < 5) do
begin
CheckDay := IncDay(CheckDay, 7);
WorkMonth := MonthOf(CheckDay);
Inc(Index);
end;
if (WorkMonth = MM) and (Index = 5) then
Result := CheckDay
else
Result := 0;
end;

//
ShowMessage(DateToStr(FifthTuesday1(8, 2011)))
``````
0

Commented:
My approach is less iterative, as far as the last Tuesday is concerned.

* Any month with less than 29 days can NEVER have a fifth of any day of the week -- I'm looking at you, February (most of the time).
* As long as the day of the week of the last day of the month minus the day-of-the-week value for Tuesday is greater than -1 and also greater than
(DayofTheMonth(LastDayOfTheMonth) - 29) then the
FifthTuesday := LastDayOfTheMonth - (DateOfWeek(LastDayOfTheMonth) - Tuesday)

In my proof-of-concept test, I passed a year to a routine that first calculated the end of January of that passed year and then incremented that date in a loop a month-at-a-time.  Applying the logic above, I either added the fifthTuesday date to a list continued iterating the subsequent 11 months in the passed year.

IncMonth() or IncAMonth() would be the function to use in the iteration.
0

Author Commented:
thanks guys,
I'm very busy right now but I'll be back later!
0

Commented:
@ewangoya & jimyX

My Delphi system is offline, so you are welcome to try your hand at the alternative approach if you wish.  I will not be posting any code.
0

Author Commented:
Hi folks,
great job! Both work exactly...
You should have shared points of course for this impressive lesson!

When I started thinking about the solution, I thought about taking the first Tuesday and add 4 weeks (28 days) and then see if we still are within respective month.

I creamed off and carved the following code.
I don't know if Delphi error ewangoya found, can cause problems there?
``````procedure TForm1.spinEditYearChange(Sender: TObject);
var i : integer;
dt,LastDay : TDate;
begin
Memo1.Clear;
for i := 1 to 12 do
begin
dt := EncodeDate(Floor(spinEditYear.Value), i, 1); // Go to 1st day
Lastday := EndOfTheMonth(dt);
while DayOfWeek(dt) <> 3 do dt := dt + 1; // Toggle to Fist Tuesday
dt := dt + 28; // Add 4 weeks to first Tuesday
if dt <= Lastday then // Check if date still in range
end;
end;
``````
0

Commented:

That works fine to me
You even saved a few iterations by adding 28 days straight to the first Tuesday
0
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