How to subtract dates?

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Hi i have the codes below, but when i run the program, the count would always stuck at zero...
eg. if i entered 3/3/2014 and daysInWeek as 4, it should return 2 for the count but it give me 0 instead. Any help would be appreciated.

C#

string datetime = txtEffectiveDate.Text;
DateTime startDate = Convert.ToDateTime(datetime); // date entered by users
int daysInWeek = Convert.ToInt32(txtDaysInWeek.Text); //no. of days entered by users
DateTime previousDate = startDate.AddDays(-daysInWeek); // date after subtracted from ori dates above

TimeSpan preDiff = previousDate - startDate;
int preDays = preDiff.Days;
 
for (var j = 0; j <= preDays; j++)
{
   var pretestDate = startDate.AddDays(-j);
   switch (pretestDate.DayOfWeek)
   {
      case DayOfWeek.Saturday:
      count++;
      break;
      case DayOfWeek.Sunday:
      count++;
      break;
 
   }
}
 
MessageBox.Show("You have " + count + " days off");

Posted 3-Mar-14 22:05pm

Jamie888

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2 solutions

Solution 2

Stepping through that code with your debugger would have shown you that your TimeSpan value was negative. Change it to:

C#

TimeSpan preDiff = startDate - previousDate;

Posted 3-Mar-14 22:34pm

Richard MacCutchan

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2014-03-03T22:31:00

Well...you don't do anything with count, unless it's a Saturday or Sunday, so you probably need to look at that, but the main problem is pretty obvious, if you quickly run trough with the debugger.
Put a breakpoint on this line:

C#

for (var j = 0; j <= preDays; j++)

And look at the value of preDays.
What is it?
Answer, -4.
And is 0 <= -4 ?
No. So your loop is never executed - as you would have seen if you had tried using the debugger to step through the code. Probably, you wanted to reverse this:

C#

TimeSpan preDiff = previousDate - startDate;

To this:

C#

TimeSpan preDiff = startDate - previousDate;

But...since this just works out the number you first thought of - daysInWeek - why do it at all?

How to subtract dates?

2 solutions

Solution 1

Solution 2

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How to subtract dates?

2 solutions

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Solution 2

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