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Add Dateutils to your uses clause 
and then use DaysBetween which requires two TDateTime values. 
Here's what the helpfile says 
 
[Delphi] function DaysBetween(const ANow: TDateTime; const AThen: TDateTime): Integer; 
Call DaysBetween to obtain the difference, in days, between two TDateTime values. DaysBetween counts only whole days. Thus, DaysBetween reports the difference between Dec 31, 1999 11:59 PM and Jan 1, 2000 11:58 PM as 0 because the difference is one minute short of an entire day. 
&nbsp; 
==== 
So you might say 
DaysNumber := DaysBetween(MyDateSelector1.date, MyDateSelector2.date); 

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Of course there is an added element of logic you'll have to use. 
Let's say the first day selector selects a day that falls on a Wednesday, and the second is the Friday. You will obviously only want the checkboxes from Wednesday Thursday and Friday to show. 
For that you can use DayOfTheWeek from dateutils, which returns a number from 1 to 7. 
Here's the syntax: 
DayOfTheWeek(const AValue: TDateTime): Word; 

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Do you have an example on how to do it? 
The daterange might start with a friday and end with a thuesday.
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Sorry didnt see the disabled part. 
Just change the checked property to enabled 
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<pre><code class="code-10 nolinks" id="code-124089">uses
 DAteutils
 
Let us assume that you're using 2 tDateTimePicker's called tDateTimePicker1 and TDateTimePicker2 to let the user select a start and finish date and that they then click a button (or you do this on the OnChange event)
 
We can use Dateutils to determine the day of the week of our start date and end date.
 
we'll declare 2 variables for our start date and end date
 
var
 StartDay : integer;
 EndDay : integer;
 i : integer; //also need a counter
 
begin
 
//First of all, if the date range is larger than 7 days, then all checkboxes are checked
if DaysBetween(DatetimePicker1.Date, DateTimePicker2.Date) &gt;= 7 then
begin
 cbMa.checked := true;
 cbDi.checked := true;
 cbWo.checked := true;
 cbDo.checked := true;
 cbVr.checked := true;
 cbZa.checked := true;
 cbZo.checked := true;
end
else
begin
 //Get the start day and end day, taking into account that the
 //stupid user may set the start date that is later than the end date.
 If DateTimePicker1.Date &gt; DateTimerPicker2.Date then
 begin
 StartDay := DayOfTheWeek(DateTimePicker2.Date);
 EndDay := DayOfTheWeek(DateTimePicker1.Date);
 end
 else
 begin
 StartDay := DayOfTheWeek(DateTimePicker1.Date);
 EndDay := DayOfTheWeek(DateTimePicker2.Date);
 end;
 
 i := StartDay;
 while i &lt;&gt; EndDay do
 begin
 case i of
 1 : cbMa.checked := true;
 2 : cbDi.checked := true;
 3 : cbWo.checked := true;
 4 : cbDo.checked := true;
 5 : cbVr.checked := true;
 6 : cbZa.checked := true;
 7 : cbZo.checked := true;
 end;
 i := i + 1;
 if i &gt; 7 then i := 1;
 end;
end;
 
//NOTE: I forget how to end case statements - I think you put an end; at the end - but anyways, you could always do 7 if ... then statements instead
</code></pre>
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..I just love waisting my time :p
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I really sorry rfwoolf. 
I closed the question to early as it seems.
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rfwoolf: 
Your solution isn't checking the checkbox for the last day. 
A small change of line 44 will do it though. 
was: while i &lt;&gt;&nbsp;EndDay do 
now: while i &lt;&gt;&nbsp;EndDay + 1 do 
 

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My bad. Yes that makes sense :)
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Sorry rfwoolf, I started to write my answer even before your first post. 
By the time I had finished and posted I saw the rest of the messages.
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It's nobody's fault :) 
And hey, you managed to do yours without dateuls, which is always remarkable, although I personally prefer the conciseness of the dateutils stuff. 

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Yeah I could probably tidy my code up a bit to be honest but it was a quick rush job :o)
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Bye the way: 
mikelittlewood also used DayOfWeek which I believe is also using DateUtils. 
Maybe rfwoolf can sleep better now. :-)
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<div class="content wysiwyg-content">
Hi, 
 
On my form I have 7 checkboxes. Each representing on weekday. 
cbMa, cbDi, cbWo, cbDo, cbVr, cbZa and cbZo. (mon-sun) 
 
On the form the user can enter a date-from and a date-to. 
If the date-range contains less then 7 days, than checkboxes representing the days of the week that are not within the date-range much be disabled. 
 
Can anybody give me a quick way to accomplish this? 
Regards, Stef
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Hi,

On my form I have 7 checkboxes. Each representing on weekday.
cbMa, cbDi, cbWo, cbDo, cbVr, cbZa and cbZo. (mon-sun)

On the form the user can enter a date-from and a date-to.
If the date-range contains less then 7 days, than checkboxes representing the days of the week that are not within the date-range much be disabled.

Can anybody give me a quick way to accomplish this?
Regards, Stef

Quick way to determine days in date-range

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