Handling Dates and Times

One of the biggest headaches a programmer can have is working with dates. Handling hours, minutes, and seconds can be as bad as working with shillings, pence, and pounds. Fortunately, Visual Basic has a number of date and time handling functions, which appear in Table 2.10-you can even add or subtract dates using those functions. VB6 programmers will notice a number of new properties in this table.

Table 2.10: Visual Basic date and time properties.
To do this	Use this
Get the current date or time	Today, Now, TimeofDay, DateString, TimeString
Perform date calculations	DateAdd, DateDiff, DatePart
Return a date	DateSerial, DateValue
Return a time	TimeSerial, TimeValue
Set the date or time	Today, TimeofDay
Time a process	Timer

Here's an example in which I'm adding 22 months to 12/31/2001 using DateAdd-you might note in particular that you can assign dates of the format 12/31/2001 to variables of the Date type if you enclose them inside # symbols:

Imports System.Math
Module Module1
    Sub Main()
        Dim FirstDate As Date
        FirstDate = #12/31/2001#
        System.Console.WriteLine("New date: " & DateAdd_
        (DateInterval.Month, 22, FirstDate))
    End Sub
End Module

Here's what you see when you run this code:

New date: 10/31/2003
Press any key to continue

There's something else you should know-the Format function makes it easy to format dates into strings, including times. For easy reference, see Table 2.11, which shows some ways to display the date and time in a string-note how many ways there are to do this.

Table 2.11: Using Format to display dates and times.
Format Expression	Yields this
Format(Now, "M-d-yy")	"1-1-03"
Format(Now, "M/d/yy")	"1/1/03"
Format(Now, "MM - dd - yy")	"01 /01 / 03"
Format(Now, "ddd, MMMM d, yyy")	"Friday, January 1, 2003"
Format(Now, "d MMM, yyy")	"1 Jan, 2003"
Format(Now, "hh:mm:ss MM/dd/yy")	"01:00:00 01/01/03"
Format(Now, "hh:mm:ss tt MM-dd-yy")	"01:00:00 AM 01-01-03"

You can also compare dates and times directly. For example, here's how you loop until the current time (returned as a string by TimeString) exceeds a certain time; when the time is up, the code beeps using the Visual Basic Beep function:

While TimeString < "15:45:00"
End While
Beep()

Tip

Don't use the above code snippet for more than an example of how to compare times! The eternal looping while waiting for something to happen is a bad idea in Windows, because your program monopolizes a lot of resources that way. Instead, set up a Visual Basic Timer and have a procedure called, say, every second.