How can I calculate number of days between 2 dates? - asp.net

Question

I have a reservation page and a reservation table which contains reservationstart column, reservationend column and numofdays column.
I have determined the number of days between the two dates which a client will select but nothing was stored in the table when I update.
The data type of numofdays was datatime but I have changed this to int.
I used this first, to declare the start and end date:
DayPilotScheduler1.Scale = TimeScale.Manual
Dim start As New Date(Date.Today.Year, 1, 1, 12, 0, 0)
Dim [end] As Date = start.AddYears(1)
This is the code for the update:
Protected Sub DayPilotScheduler1_EventMove(ByVal sender As Object, ByVal e As DayPilot.Web.Ui.Events.EventMoveEventArgs)
Dim id_Renamed As String = e.Value
Dim start As Date = e.NewStart
Dim [end] As Date = e.NewEnd
Dim resource As String = e.NewResource
Dim message As String = Nothing
If Not dbIsFree(id_Renamed, start, [end], resource) Then
message = "The reservation cannot overlap with an existing reservation."
ElseIf e.OldEnd <= Date.Today Then
message = "This reservation cannot be changed anymore."
ElseIf e.OldStart < Date.Today Then
If e.OldResource <> e.NewResource Then
message = "The room cannot be changed anymore."
Else
message = "The reservation start cannot be changed anymore."
End If
ElseIf e.NewStart < Date.Today Then
message = "The reservation cannot be moved to the past."
Else
dbUpdateEvent(id_Renamed, start, [end], resource)
'message = "Reservation moved.";
End If
LoadResourcesAndEvents()
DayPilotScheduler1.UpdateWithMessage(message)
End Sub
Private Sub dbUpdateEvent(ByVal id As String, ByVal start As Date, ByVal [end] As Date, ByVal resource As String)
Using con As New SqlConnection(ConfigurationManager.ConnectionStrings("connectionStringLocal").ConnectionString)
con.Open()
Dim numOfDay As Integer = CInt(([end] - start).TotalDays())
Dim cmd As New SqlCommand("UPDATE [Reservation] SET ReservationStart = #start, ReservationEnd = #end, RoomId = #resource,numofday=#numofday WHERE ReservationId = #id", con)
cmd.Parameters.AddWithValue("id", id)
cmd.Parameters.AddWithValue("start", start)
cmd.Parameters.AddWithValue("end", [end])
cmd.Parameters.AddWithValue("resource", resource)
cmd.Parameters.Add("numofday", SqlDbType.Int).Value = numOfDay
cmd.ExecuteNonQuery()
End Using
End Sub
Screenshot of database table structure:

Answer 1

Math.floor(Math.abs(new Date(timestringone) - new Date(timestringtwo))/(1000*60*60*24))
Simply subtracting the dates returns the time in Milliseconds inbetween them. If the first time was before the second time the value is negative, so i used Math.abs to make it absolute. Then we divide trough 1000Milliseconds=1second, 60seconds=1minute, 60minutes=1hour, 24hours=1 day, and floor it to whole days. Requires two valid timestrings (timestringone and timestringtwo) to be given.
This is a javascript solution as youve included the js tag...

Answer 2

I am not sure about the VB.Net but you can easily accomplished it in C# using an object of Type "TimeSpan". For example: let's assume that we want to know the number of days between the start and end. values for the DateTime Type and show it in a Console window, then I may write something like:
DateTime start=DateTime.MinValue;
DateTime end=DateTime.MaxValue;
TimeSpan span=end-start;
Console.WriteLine( "There're {0} days between {1} and {2}" , span.TotalDays, start.ToString(), end.ToString() );

Answer 3

OP is having problems using the .Days property on the TimeSpan structure. I think this may help:
Dim numOfDay As Integer = CInt(([end] - start).TotalDays())
The output is:
365
Moving onto the use of your parameters, I think you would benefit from using .Add and specifying the data type:
cmd.Parameters.Add("#id", SqlDbType.Int).Value = id
cmd.Parameters.Add("#start", SqlDbType.Date).Value = start
cmd.Parameters.Add("#end", SqlDbType.Date).Value = [end]
cmd.Parameters.Add("#resource", SqlDbType.Int).Value = CInt(resource)
cmd.Parameters.Add("#numofday", SqlDbType.Int).Value = numOfDay
Note that you may have to change the SqlDbType. I've taken an assumption.
I would also implement Using for both the SqlConnection and SqlCommand. This for me is just good practice and the code does read better. I would also use the .Add overload for all parameters.
Using con As New SqlConnection(ConfigurationManager.ConnectionStrings("connectionStringLocal").ConnectionString),
cmd As New SqlCommand("UPDATE [Reservation] SET ReservationStart = #start, ReservationEnd = #end, RoomId = #resource, numofday = #numofday WHERE ReservationId = #id", con)
con.Open()
cmd.Parameters.Add("#id", SqlDbType.Int).Value = id
cmd.Parameters.Add("#start", SqlDbType.Date).Value = start
cmd.Parameters.Add("#end", SqlDbType.Date).Value = [end]
cmd.Parameters.Add("#resource", SqlDbType.Int).Value = CInt(resource)
cmd.Parameters.Add("#numofday", SqlDbType.Int).Value = CInt(([end] - start).TotalDays())
Dim rowsAffected As Integer = cmd.ExecuteNonQuery()
If rowsAffected = 0 Then
'nothing updated
Else
'something updated
End If
End Using