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Date and Time Values

Introduction to Date Values

Introduction

A date is a non-spatial value that uses a combination of numbers, symbols, and strings (or names). Both the Visual Basic language and the .NET Framework provide tremendous support for date and time values.

The Date Data Type

To support dates and time values, the Visual Basic library includes a shared (or static) class named DateAndTime. Because this is a shared class, all of its members are directly accessible when you write VB code. If a member you want to access has the same name as a class or an enumeration in the .NET Framework, then you must qualify it.

In the Visual Basic language, the DateAndTime class is represented by a data type named Date. To support dates and time values, the .NET Framework provides a structure named DateTime that is defined in the System namespace.

The Date data type and the DateTime structure support dates and time starting from January 1st, 0001 at midnight (0:00:00 AM) up to December 31st, 9999 at midnight minus 1 second (1!:59:59 PM).

Introduction to Date Values

Creating a Date Value

To create a date or a time value, declare a variable using either the Date data type or the DateTime structure. Here is an example:

<%
Dim DateHired As Date
%>

There are various ways you can initialize a date or time variable. The numbers are represented with:

  • Y (or y) for a digit in a year
  • M (or m) for a digit in a month
  • D (or d) for a digit in a day
  • A separator: This can be - or /. Only one type of separator can be used in a value

When initializing the variable, if you want to provide a constant value, you can include it between # and #. The value can use the following formula: MM-DD-YYYY: Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim DateHired As Date

DateHired = #08-22-2018#

Response.Write("Date Hired: " & DateHired)
%>
</body>
</html>

This would produce:

Creating a Date Value

You can also use the date formula as MM/DD/YYYY.

As an alternative to initiate the variable, the Visual Basic language provides a function named DateSerial. Its syntax is:

Public Shared Function DateSerial(Year As Integer,
				  Month As Integer,
				  Day As Integer) As Date

Here is an example:

<%
Dim DateHired = DateSerial(2018, 8, 22)

Response.Write("Date Hired: " & DateHired)
%>

As one more alternative, the DateTime structure is equipped with the following contstructor:

Public Sub New(year As Integer, month As Integer, day As Integer)

Here is an example:

<%
Dim DateHired As Date

DateHired = New DateTime(2018, 8, 22)

Response.Write("Date Hired: " & DateHired)
%>
</body>
</html>

Converting a Value to Date or Time

To let you convert a value to date or time, the Visual Basic language provides a function named CDate. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim show = "05-30-2018"
    Dim depart = CDate("07/23/2017")

    Dim d = CDate(show)

    Response.Write("The TV show will premiere on " & d & ".")
    Response.Write("<br>The cruise session will start on " & depart & ".")
%>

</body>
</html>

This would produce:

Converting a Value to Date or Time

As an alternative, you can use a function named DateValue. Its syntax is:

Public Shared Function DateValue(StringDate As String) As Date

Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim show = "05-30-2018"
    Dim depart = DateValue("07/23/2017")

    Dim d = DateValue(show)

    Response.Write("The TV show will premiere on " & d & ".")
    Response.Write("<br>The cruise session will start on " & depart & ".")
%>

</body>
</html>

The Current System Date

To let you get the current date of the computer that a visitor is using, use a property named Today:

Public Shared Property Today As Date

As an alternative, the Visual Basic language provides a property named DateString:

Public Shared Property DateString As String

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<script runat="server">
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    Dim dteStart = DateSerial(2016, 8, 1)

    txtStartDate.Text = dteStart
End Sub

Sub btnSubmitTimeSheetClick(ByVal sender As Object, ByVal e As EventArgs)

End Sub
</script>
<title>Employee Time Sheet</title>
</head>
<body>
<h3>Employee Time Sheet</h3>

<form id="frmTimeSheet" runat="server">
<table style="width: 500px">
  <tr>
    <td Width="100px"><b>Employee #:</b></td>
    <td Width="100px">
    	<asp:TextBox id="txtEmployeeNumber" Width="70px"
    	             runat="server" AutoPostBack="True"></asp:TextBox></td>
    <td><asp:TextBox id="txtEmployeeName"
    	             runat="server" Width="192px"></asp:TextBox></td>
  </tr>
</table>
<table>
  <tr>
    <td Width="100px"><b>Start Date:</b></td>
    <td><asp:TextBox id="txtStartDate" Width="70px"
    		     runat="server"></asp:TextBox></td>
    <td><b>End Date:</b></td>
    <td><asp:TextBox id="txtEndDate" runat="server"></asp:TextBox></td>
  </tr>
</table>
<br>
<br>
<table width="520">
  <tr>
    <td style="text-align: center">
	    <asp:Button id="btnSubmitTimeSheet" Text="Submit Time Sheet"
            OnClick="btnSubmitTimeSheetClick"
                        runat="server"></asp:Button></td>
  </tr>
</table>
</form>
</body>
</html>

Here is an example of displaying the webpage:

Creating a Date Value

Formatting the Display of Dates

Introduction

To assist you in controlling how a date value should display, the Visual Basic language provides a function named FormatDateTime. Its syntax is:

Public Shared Function FormatDateTime(Expression As Date,
				      NamedFormat As DateFormat) As String

As we saw in previous lessons, the language also provides a function named Format. As a reminder, its syntax is:

Public Shared Function Format(Expression As Object, Style As String) As String

In both cases, the first argument is the date value that will be formatted. The second argument specifies the format.

The DateTime structure provides additional means.

The Short Date Format

To display the short date format, pass the second argument of the FormatDateTime() function as DateFormat.ShortDate. Here is an example:

<%
Dim happy As Date

happy = DateString

Response.Write("Happy Birthday: " & FormatDateTime(happy, DateFormat.ShortDate))
%>

As an alternative, pass the second argument of the Format() function as d (lowercase). Here is an example:

<%
Dim happy As Date

happy = DateString

Response.Write("Happy Birthday: " & Format(happy, "d"))
%>

The Long Date Format

To display the long date format, pass the second argument of the FormatDateTime() function as DateFormat.LongDate. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<script runat="server">
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    Dim dteStart = DateSerial(2016, 8, 1)

    txtStartDate.Text = FormatDateTime(dteStart, DateFormat.ShortDate)

    txtEndDate.Text = FormatDateTime(dteStart, DateFormat.LongDate)
End Sub

Sub btnSubmitTimeSheetClick(ByVal sender As Object, ByVal e As EventArgs)

End Sub
</script>
<title>Employee Time Sheet</title>
</head>
<body>
<h3>Employee Time Sheet</h3>

<form id="frmTimeSheet" runat="server">
<table style="width: 500px">
  <tr>
    <td Width="100px"><b>Employee #:</b></td>
    <td Width="100px">
    	<asp:TextBox id="txtEmployeeNumber" Width="70px"
    	             runat="server" AutoPostBack="True"></asp:TextBox></td>
    <td><asp:TextBox id="txtEmployeeName"
    	             runat="server" Width="230px"></asp:TextBox></td>
  </tr>
</table>
<table>
  <tr>
    <td Width="100px"><b>Start Date:</b></td>
    <td><asp:TextBox id="txtStartDate" Width="70px"
    		     runat="server"></asp:TextBox></td>
    <td><b>End Date:</b></td>
    <td><asp:TextBox id="txtEndDate" Width="180px"
    		     runat="server"></asp:TextBox></td>
  </tr>
</table>
<br>
<br>
<table width="520">
  <tr>
    <td style="text-align: center">
	    <asp:Button id="btnSubmitTimeSheet" Text="Submit Time Sheet"
            OnClick="btnSubmitTimeSheetClick"
                        runat="server"></asp:Button></td>
  </tr>
</table>
</form>
</body>
</html>

Here is an example of displaying the webpage:

Creating a Date Value

As an alternative, pass the second argument of the Format() function as D (uppercase). Here is an example:

<%
Dim happy As Date

happy = DateString

Response.Write("Happy Birthday: " & Format(happy, "D"))
%>

Here is an example of displaying the webpage:

Creating a Date Value

The Format() function provides more options to control has a date or one of its components (day, month, and/or year) appear.

The Parts of a Date

Introduction to the Part Name of a Date Value

The Visual Basic language provides various options to get the day, the month, or the year of an existing date value. One of the functions used is named DatePart. It is available in two versions whose syntaxes are:

Public Shared Function DatePart(Interval As DateInterval,
				DateValue As Date,
				FirstDayOfWeekValue As FirstDayOfWeek,
				FirstWeekOfYearValue As FirstWeekOfYear) As Integer
Public Shared Function DatePart(Interval As String,
				DateValue As Object,
				DayOfWeek As FirstDayOfWeek,
				WeekOfYear As FirstWeekOfYear) As Integer

The first argument, required, specifies the type of value to get. The second argument, also required, is the date from which to get the value.

The Format() function provides other ways to get the parts of a date value.

The Day of a Date

To get the day in the month of a date value, you can call a function named Day. Its syntax is:

Public Shared Function Day(DateValue As Date) As Integer

This function takes a date as argument and produces its day. Here is an example:

<%
Dim dob As Date = #02/12/1975#

Dim d = Day(dob)
Response.Write("Day: " & d)
%>

As an alternative, the DateTime structure is equipped with a property named Day:

Public ReadOnly Property Day As Integer

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim current As Date = #11/24/2006#

    Dim day = current.Day

    Select Case day
        Case 1, 21, 31
            Response.Write("The date occurs on the " & day & "<sup>st</sup>")
        Case 2, 22
            Response.Write("The date occurs on the " & day & "<sup>nd</sup>")
        Case 3, 23
            Response.Write("The date occurs on the " & day & "<sup>rd</sup>")
        Case Else
            Response.Write("The date occurs on the " & day & "<sup>th</sup>")
    End Select
%>

</body>
</html>

This would produce:

The Day of a Date

As one more alternative, you can call the DatePart() function. Pass the second argument as either DateInterval.Day or "d". Here is an example:

<%
    Dim dob As Date = #02/12/1975#

    Dim d = DatePart(DateInterval.Day, dob)
    Response.Write("Day: " & d)

    d = DatePart("d", dob)
    Response.Write("<br>Day: " & d)
%>

One more alternative is to cass the Format() function and pass the second argument as "dd". Here is an example:

<%
    Dim dob As Date = #02/12/1975#

    Dim d = Format(dob, "dd")
    Response.Write("<br>Day: " & d)
%>

The Month Name of a Date

To let you get the name of the month of a date, the Visual Basic language provides a function named Month. Its syntax is:

Public Shared Function MonthName(Month As Integer, Abbreviate As Boolean) As String

The first argument is required and it is just the numeric position of a month within a year. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Response.Write("Month: " & MonthName(8))
%>
</body>
</html>

This would produce:

The Month of a Date

As you can see, if you provide only the first argument, the full name of the month is produced. If you want a short name for the month, pass the second argument as True.

The Numeric Month of a Date

To get the numeric position of a month in a date, you can call a function named Month. Its syntax is:

Public Shared Function Month(DateValue As Date) As Integer

Here is an example:

<%
    Dim vote = #02/20/2016#
    Response.Write("Month: " & Month(vote))
%>

As you can see, the Month() function returns an integer that is the position or index of the month. You can pass that return value to the MonthName() function. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim vote = #02/20/2016#
    Response.Write("Month: " & MonthName(Month(vote)))
%>
</body>
</html>

This would produce:

The Numeric Month of a Date

As an alternative, the DateTime structure is equipped with a property named Month:

Public ReadOnly Property Month As Integer

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim current As Date = #11/24/2006#

    Dim day = current.Day

    Select Case day
        Case 1, 21, 31
            Response.Write("The date occurs on the " & day & "<sup>st</sup>")
        Case 2, 22
            Response.Write("The date occurs on the " & day & "<sup>nd</sup>")
        Case 3, 23
            Response.Write("The date occurs on the " & day & "<sup>rd</sup>")
        Case Else
            Response.Write("The date occurs on the " & day & "<sup>th</sup>")
    End Select

    Response.Write(" in " & MonthName(current.Month))
%>

</body>
</html>

This would produce:

The Numeric Month of a Date

As one more alternative, you can call the DatePart() function. Pass the first argument as either DateInterval.Month, "m", or "M" Here is an example:

<%
    Dim vote = #02/20/2016#
    Response.Write("Month: " & DatePart(DateInterval.Month, vote))
%>

As another alternative, you can call the Format function and pass the second argument as "MM". Here is an example:

<%
    Dim vote = #02/20/2016#
    Response.Write("Month: " & Format(vote, "MM"))
%>

You can call the Day(), the Month(), the MonthName(), or the DatePart() function as many times as you want to create a combination of values. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim dteStart = DateSerial(2016, 8, 1)
Response.Write("Date Considered: " & Month(dteStart) & "-" & Day(dteStart))
Response.Write("<br>Important Date: " & DatePart(DateInterval.Month, dteStart)
		& "-" &	DatePart(DateInterval.Day, dteStart))
Response.Write("<br>To Note in Calendar: " & MonthName(Month(dteStart))
		& ", " & DatePart(DateInterval.Day, dteStart))
%>

</body>
</html>

This would produce:

Formatting a Date

One of the advantages of the Format() function is that it already has that functionality built-in. This means that you can combine letters and symbols in the second argument of that function. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<script runat="server">
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
        Dim dteStart = DateSerial(2016, 8, 1)

        txtStartDate.Text = FormatDateTime(dteStart, DateFormat.ShortDate)
        txtEndDate.Text = FormatDateTime(dteStart, DateFormat.LongDate)

        lblWeek1Monday.Text = Format(dteStart, "MM-dd")
End Sub

Sub btnSubmitTimeSheetClick(ByVal sender As Object, ByVal e As EventArgs)

End Sub
</script>
<style>
#container
{
    margin: auto;
    width:  auto;
}
</style>
<title>Salary Estimation</title>
</head>
<body>
<div id="container">

<h3>Employee Time Sheet</h3>

<form id="frmTimeSheet" runat="server">
<table style="width: 500px">
  <tr>
    <td Width="100px"><b>Employee #:</b></td>
    <td Width="100px">
    	<asp:TextBox id="txtEmployeeNumber" Width="70px"
    	             runat="server" AutoPostBack="True"></asp:TextBox></td>
    <td><asp:TextBox id="txtEmployeeName"
    	             runat="server" Width="230px"></asp:TextBox></td>
  </tr>
</table>
<table>
  <tr>
    <td Width="100px"><b>Start Date:</b></td>
    <td><asp:TextBox id="txtStartDate" Width="70px"
    		     runat="server"></asp:TextBox></td>
    <td><b>End Date:</b></td>
    <td><asp:TextBox id="txtEndDate" Width="180px" runat="server"></asp:TextBox></td>
  </tr>
</table>
<br>
<br>
<table>
  <tr>
    <td>&nbsp;</td>
    <td><asp:Label id="lblWeek1Monday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Tuesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Wednesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Thursday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Friday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Saturday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Sunday" runat="server"></asp:Label></td>
  </tr>
  <tr>
    <td><b>Week 1:</b></td>
    <td><asp:TextBox id="txtWeek1Monday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Tuesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Wednesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Thursday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Friday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Saturday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Sunday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
  </tr>
  <tr>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
  </tr>
  <tr>
    <td>&nbsp;</td>
    <td><asp:Label id="lblWeek2Monday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Tuesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Wednesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Thursday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Friday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Saturday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Sunday" runat="server"></asp:Label></td>
  </tr>
  <tr>
    <td><b>Week 2:</b></td>
    <td><asp:TextBox id="txtWeek2Monday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Tuesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Wednesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Thursday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Friday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Saturday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Sunday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
  </tr>
</table>
<br>
<br>
<table width="520">
  <tr>
    <td style="text-align: center">
	    <asp:Button id="btnSubmitTimeSheet" Text="Submit Time Sheet"
            OnClick="btnSubmitTimeSheetClick"
                        runat="server"></asp:Button></td>
  </tr>
</table>
</form>
    </div>
</body>
</html>

This would produce:

Formatting a Date

The Year of a Date

To let you get the year of a date, the Visual Basic language provides a function named Year. Its syntax is:

Public Shared Function Year(DateValue As Date) As Integer

Here is an example:

<%
Dim dteStart = DateSerial(2016, 8, 1)
Response.Write("Year Considered: " & Year(dteStart))
%>

As an alternative, the DateTime structure is equipped with a property named Year:

Public ReadOnly Property Year As Integer

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim current As Date = #11/24/2006#

    Dim day = current.Day

    Select Case day
        Case 1, 21, 31
            Response.Write("The date occurs on the " & day & "<sup>st</sup>")
        Case 2, 22
            Response.Write("The date occurs on the " & day & "<sup>nd</sup>")
        Case 3, 23
            Response.Write("The date occurs on the " & day & "<sup>rd</sup>")
        Case Else
            Response.Write("The date occurs on the " & day & "<sup>th</sup>")
    End Select

    Response.Write(" day of " & MonthName(current.Month))
    Response.Write(" in " & current.Year)
%>

</body>
</html>

This would produce:

The Year of a Date

Another way to get the year value is to call the DatePart() function. Pass the first argument as either DateInterval.Year or "yyyy". Here is an example:

<%
Dim dteStart = DateSerial(2016, 8, 1)
Response.Write("Year Considered: " & DatePart(DateInterval.Year, dteStart))
%>

One more alternative is to call the Format() function and pass the second argument as "yyy".

The Week Day

To let you get the index of a day of the week in which a date occurs, the Visual Basic language provides the Weekday() function. Its syntax is:

Public Shared Function Weekday(DateValue As Date,
			       DayOfWeek As FirstDayOfWeek) As Integer

The first argument is required and is a date that will be considered. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim dteStart = DateSerial(2016, 8, 1)

Response.Write("On " & dteStart & ", the day of the week is " & Weekday(dteStart))
%>

</body>
</html>

This would produce:

The Week Day

The date of August 1st, 2016 is on a Monday. This means that the date system of the Visual Basic language considers Sunday as the first day of the week. If you want the week of your application to start on a different day, pass the second argument, wihch is a member of the FirstDayOfWeek enumeration. The members are: FirstDayOfWeek.System as 0, FirstDayOfWeek.Sunday as 1, FirstDayOfWeek.Monday as 2, FirstDayOfWeek.Tuesday as 3, FirstDayOfWeek.Wednesday as 4, FirstDayOfWeek.Thursday as 5, FirstDayOfWeek.Friday as 6, and FirstDayOfWeek.Saturday as 7.

To let you get the name of a day in a week, the Visual Basic language provides a function named WeekdayName. Its syntax is:

Public Shared Function WeekdayName(Weekday As Integer,
				   Abbreviate As Boolean,
				   FirstDayOfWeekValue As FirstDayOfWeek) As String

The first argument is the only one required. It is the numeric index of a day in a week. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Response.Write("Week Day Name: " & WeekDayName(1))
%>

</body>
</html>

This would produce:

The Week Day

As you can see, by default, this function produces the full name of a week day. If you want a short name, pass the second argument as True. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Response.Write("Week Day Name: " &  WeekDayName(4, True))
%>

</body>
</html>

This would produce:

The Week Day

The third argument follows the same logic as the second argument of the Weekday() function.

 
 
 

Operations on Date Values

Adding a Number to a Date Value

Date addition consists of adding a number of days, months, or years, to a date value. To support this operation, the Visual Basic language provides a function named DateAdd. It is overloaded in two versions. The syntax of one of them is:

Public Shared Function DateAdd(Interval As String,
			       Number As Integer,
			       DateValue As Object) As Date

The other version uses the following syntax:

Public Shared Function DateAdd(Interval As DateInterval,
			       Number As Integer,
			       DateValue As Date) As Date

The first argument specifies the type of value that will be added. It can be one of the following values:

Date Interval String Description
DateInterval.Day d A number of days to add to the date value
DateInterval.DayOfYear y A number of days of a year will be added to the date value
DateInterval.Week w A number of weeks will be added to the date value
DateInterval.Week ww A number of weeks will be added to the date value
DateInterval.Month m A number of months will be added to the date value
DateInterval.Year yyyy A number of years to add be added to the date value
DateInterval.quarter q A number of quarters of a year will be added to the date value

Here is an example that adds a number of years to a date value:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim dob As Date = #02/12/1975#
    Dim happy = DateString

    Dim passed = DateAdd("yyyy", 2, dob)
    Response.Write("Happy Birthday: " & passed)
%>
</body>
</html>

This would produce:

Date Addition

Once a number has been added to a date value, the function produces a new date. You can format it any way you want. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<script runat="server">
Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
        Dim dteStart = DateSerial(2016, 8, 29)

        txtStartDate.Text = FormatDateTime(dteStart, DateFormat.ShortDate)
        txtEndDate.Text = FormatDateTime(DateAdd(DateInterval.Day, 13, dteStart), DateFormat.LongDate)

        lblWeek1Monday.Text = Format(dteStart, "MM-dd")
        lblWeek1Tuesday.Text = Format(DateAdd(DateInterval.Day, 1, dteStart), "MM-dd")
        lblWeek1Wednesday.Text = Format(DateAdd(DateInterval.Day, 2, dteStart), "MM-dd")
        lblWeek1Thursday.Text = Format(DateAdd(DateInterval.Day, 3, dteStart), "MM-dd")
        lblWeek1Friday.Text = Format(DateAdd(DateInterval.Day, 4, dteStart), "MM-dd")
        lblWeek1Saturday.Text = Format(DateAdd(DateInterval.Day, 5, dteStart), "MM-dd")
        lblWeek1Sunday.Text = Format(DateAdd(DateInterval.Day, 6, dteStart), "MM-dd")

        lblWeek2Monday.Text = Format(DateAdd(DateInterval.Day, 7, dteStart), "MM-dd")
        lblWeek2Tuesday.Text = Format(DateAdd(DateInterval.Day, 8, dteStart), "MM-dd")
        lblWeek2Wednesday.Text = Format(DateAdd(DateInterval.Day, 9, dteStart), "MM-dd")
        lblWeek2Thursday.Text = Format(DateAdd(DateInterval.Day, 10, dteStart), "MM-dd")
        lblWeek2Friday.Text = Format(DateAdd(DateInterval.Day, 11, dteStart), "MM-dd")
        lblWeek2Saturday.Text = Format(DateAdd(DateInterval.Day, 12, dteStart), "MM-dd")
        lblWeek2Sunday.Text = Format(DateAdd(DateInterval.Day, 13, dteStart), "MM-dd")
End Sub

Sub btnSubmitTimeSheetClick(ByVal sender As Object, ByVal e As EventArgs)

End Sub
</script>
<style>
#container
{
    margin: auto;
    width:  auto;
}
</style>
<title>Salary Estimation</title>
</head>
<body>
<div id="container">

<h3>Employee Time Sheet</h3>

<form id="frmTimeSheet" runat="server">
<table style="width: 500px">
  <tr>
    <td Width="100px"><b>Employee #:</b></td>
    <td Width="100px">
    	<asp:TextBox id="txtEmployeeNumber" Width="70px"
    	             runat="server" AutoPostBack="True"></asp:TextBox></td>
    <td><asp:TextBox id="txtEmployeeName"
    	             runat="server" Width="230px"></asp:TextBox></td>
  </tr>
</table>
<table>
  <tr>
    <td Width="100px"><b>Start Date:</b></td>
    <td><asp:TextBox id="txtStartDate" Width="70px"
    		     runat="server"></asp:TextBox></td>
    <td><b>End Date:</b></td>
    <td><asp:TextBox id="txtEndDate" Width="180px" runat="server"></asp:TextBox></td>
  </tr>
</table>
<br>
<br>
<table>
  <tr>
    <td>&nbsp;</td>
    <td><asp:Label id="lblWeek1Monday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Tuesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Wednesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Thursday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Friday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Saturday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek1Sunday" runat="server"></asp:Label></td>
  </tr>
  <tr>
    <td><b>Week 1:</b></td>
    <td><asp:TextBox id="txtWeek1Monday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Tuesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Wednesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Thursday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Friday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Saturday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek1Sunday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
  </tr>
  <tr>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
    <td>&nbsp;</td>
  </tr>
  <tr>
    <td>&nbsp;</td>
    <td><asp:Label id="lblWeek2Monday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Tuesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Wednesday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Thursday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Friday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Saturday" runat="server"></asp:Label></td>
    <td><asp:Label id="lblWeek2Sunday" runat="server"></asp:Label></td>
  </tr>
  <tr>
    <td><b>Week 2:</b></td>
    <td><asp:TextBox id="txtWeek2Monday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Tuesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Wednesday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Thursday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Friday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Saturday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
    <td><asp:TextBox id="txtWeek2Sunday" Text="0.00" Width="60px" runat="server"></asp:TextBox></td>
  </tr>
</table>
<br>
<br>
<table width="520">
  <tr>
    <td style="text-align: center">
	    <asp:Button id="btnSubmitTimeSheet" Text="Submit Time Sheet"
            OnClick="btnSubmitTimeSheetClick"
                        runat="server"></asp:Button></td>
  </tr>
</table>
</form>
    </div>
</body>
</html>

This would produce

Adding a Number to a Date Value

To let you add a number of years to a date, the DateTime structure is equipped with a method named AddYears. Its syntax is:

Public Function AddYears(value As Integer) As Date

To let you add a number of months to a date, the DateTime structure is equipped with a method named AddMonths. Its syntax is:

Public Function AddMonths(months As Integer) As Date

To let you add a number of days to a date, the DateTime structure is equipped with a method named AddDays. Its syntax is:

Public Function AddDays(value As Double) As Date

To add a number of days, pass it as an integer. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim vacationFrom As Date
    Dim vacationEnd As Date

    vacationFrom = #12-19-2016#
    vacationEnd = vacationFrom.AddDays(25)

    Response.Write("The boss will be on vacation for 2 weeks from " &
                   FormatDateTime(vacationFrom, DateFormat.LongDate) &
                   " to " & FormatDateTime(vacationEnd, DateFormat.LongDate) & ".")
%>

</body>
</html>

This would produce

Adding a Number to a Date Value

To add a number of days and a fraction of an additional day, pass a decimal number.

The Difference Between Two Date Values

To let you find the difference between two dates, the Visual Basic language provides a function named DateDiff. Its syntax is:

Public Shared Function DateDiff(Interval As DateInterval,
				Date1 As Date,
				Date2 As Date,
				DayOfWeek As FirstDayOfWeek,
				WeekOfYear As FirstWeekOfYear) As Long

The first argument specifies the type of value the function must produce. This argument uses the same value as those of the DateAdd() function. The second argument is the starting date. The third argument is the end date. Those three arguments are the only ones required. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim dteStart = DateSerial(2006, 8, 15)
Dim dteEnd = DateSerial(2018, 12, 1)

Dim days = DateDiff(DateInterval.Day, dteStart, dteEnd)
Dim months = DateDiff(DateInterval.Month, dteStart, dteEnd)
Dim years = DateDiff(DateInterval.Year, dteStart, dteEnd)

Response.Write("It took " & days & " days, or " & months &
        " months, or " & years & " years from " & dteStart & " to " & dteEnd & ".")
%>

</body>
</html>

This would produce

The Difference Between Two Date Values

To subtract a number of years (or months, or days) to a date, call the DateTime.AddYears() (DateTime.AddMonths() or DateTime.AddDays()) and pass a negative value. To subtract a number of and a portion, pass a floating-point number.

Introduction to Time Values

Overview

To support time values, the Visual Basic language uses the same Date data type used for dates. In the same way, the DateTime structure of the .NET Framework is used for time values.

Creating a Time Value

You can use the Date data type to declare a time-based variable and initialize it. The value of the variable can be included  between # and # and it can use one of the following formulas:

hh:mm
hh:mm:ss
hh:mm:ss[.fractional seconds]

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim meetingTime As Date

meetingTime = #09:35#

Response.Write("The meeting will start at " & meetingTime & ".")
%>

</body>
</html>

This would produce

Introduction to Time Values

As an alternative to create a time value, the Visual Basic language provides a function named TimeSerial. Its syntax is:

Public Shared Function TimeSerial(Hour As Integer,
				  Minute As Integer, Second As Integer) As Date

Here is an example of calling this function:

<%
Dim meetingTime As Date

meetingTime = TimeSerial(9, 35, 0)

Response.Write("The meeting will start at " & meetingTime & ".")
%>

The Current System Time

To let you get the current time of the computer that a visitor is using, the Visual Basic language provides a property named TimeString:

Public Shared Property TimeString As String

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Response.Write("The current time is " & TimeString)
%>

</body>
</html>

As an option, the Visual Basic language provides a property named TimeOfDay:

Public Shared Property TimeOfDay As Date

Here is an example of using it:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Response.Write("Time of Day: " & TimeOfDay)
%>

</body>
</html>

The Parts of a Time Value

The AM/PM Sides of a Time Value

As you may know, the hours of a time value use a 24-hour range from 0 to 23 but divided in two sections of 12 hours each. To express the first section, you can write the number between 0 and 11 as we have done in the above two examples. To re-enforce the idea that the time occurs in the morning, end the value with AM. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim late = #12:46 AM#
Dim occurring = #03:18 AM#

Response.Write("The late night TV show will end at " & late & ".")
Response.Write("<br>The event will occur in local time at " & occurring & ".")
%>

</body>
</html>

This would produce

Introduction to Time Values

The last section, also referred to as afternoon, can be expressed in two ways:

  • If you are assigning a constant time value to a variable, you can express the hour value from 12, 1, 2, etc up to 11; but then you must end the value with PM. Here are examples:
    <%@ Page Language="VB" %>
    
    <!DOCTYPE html>
    <html>
    <head>
    <title>Exercise</title>
    </head>
    <body>
    
    <%
        Dim course = #12:35 PM#
        Dim game = #03:25 PM#
    
        Response.Write("The course will start at " & course & ".")
        Response.Write("<br>The game will take place at " & game & ".")
    %>
    
    </body>
    </html>
    This would produce

    Introduction to Time Values

    In the absence of the PM section, the time is considered to occur in the morning
  • You can use the military time in which the hour is expressed as a value between 0 and 23 (0 to 11 in the morning and 12 to 23 in the afternoon/evening) and you must omit PM. Here are examples:
    <%@ Page Language="VB" %>
    
    <!DOCTYPE html>
    <html>
    <head>
    <title>Exercise</title>
    </head>
    <body>
    
    <%
        Dim course = #10:25#
        ' This value may not work with some compilers
        Dim game = #17:25#
        Dim arrival = TimeSerial(19, 48, 0)
    
        Response.Write("The course will start at " & course & ".")
        Response.Write("<br>The game will take place at " & game & ".")
        Response.Write("<br>The train will arrive at " & arrival & ".")
    %>
    
    </body>
    </html>
    This would produce

    Introduction to Time Values

To let you extract the parts of a time value, the Visual Basic language provides the the DatePart() function. The Format() function provides other options. The language also includes functions to get the hours, the minutes, and the seconds portions.

The Hour, the Minute, and the Second of a Time

To let you get the hours, the minutes, and the seconds portions of a time value, the Visual Basic language provides functions named Hour, Minute, and Second. Their syntaxes are:

Public Shared Function Hour(TimeValue As Date) As Integer
Public Shared Function Minute(TimeValue As Date) As Integer
Public Shared Function Second(TimeValue As Date) As Integer

Here are examples of calling them:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim occurrence As Date = #12:35:48 AM#

    Response.Write("The event occurs at " & Hour(occurrence) & "." &
                   Minute(occurrence) & "." & Second(occurrence))
%>

</body>
</html>

This would produce:

The Hour, the Minute, and the Second of a Time

An alternative is to call the DatePart() function. Pass the first argument as

  • DateInterval.Hour or "h" for the hour
  • DateInterval.Minute or "n" for the hour
  • DateInterval.Second or "h" for the hour

Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim occurrence As Date = #12:35:48 AM#

    Response.Write("The event occurs at " &
                   DatePart(DateInterval.Hour, occurrence) & "." &
                   DatePart(DateInterval.Minute, occurrence) & "." &
                   DatePart(DateInterval.Second, occurrence))
%>

</body>
</html>

One more alternative is to cass the Format() function and pass the second argument as "%h" for the hour, "%m" for the minute, or "%s" for the second. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim occurrence As Date = #10:35:48 AM#

    Response.Write("The event occurs at " &
                   Format(occurrence, "%h") & "." &
                   Format(occurrence, "%m") & "." &
                   Format(occurrence, "%s"))
%>

</body>
</html>

Converting a Value to Time

To convert an appropriately-formatted value to time, you can call the same CDate() function used for date values. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim late As String = "12:35 AM"
    Dim occurring As String = "#03:18 AM#"

    Dim d = CDate(late)
    Dim o = CDate(occurring)

    Response.Write("The late night TV show will end at " & d & ".")
    Response.Write("<br>The event occur in local time at " & o & ".")
%>

</body>
</html>

If the time is provided as a string, you can convert it using a function named TimeValue. Its syntax is

Public Shared Function TimeValue(StringTime As String) As Date

Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim late = "12:35 AM"
    Dim occurring = TimeValue("03:18 AM")

    Dim d = TimeValue(late)

    Response.Write("The late night TV show will end at " & d & ".")
    Response.Write("<br>The event occur in local time at " & occurring & ".")
%>

</body>
</html>

Formatting the Display of a Time Value

Introduction

To let you control how a time value should appear, you can use the same FormatDateTime() used for date value. The Format() function also is available with additional options. The DateTime structure provides other options.

The Short Time Format

To display a time value in a short format, pass the second argument of the FormatDateTime() function as DateFormat.ShortTime. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim late As String = "12:35 AM"
Dim occurring As String = "#03:18 AM#"

Dim d = CDate(late)
Dim o = CDate(occurring)

Response.Write("The late night TV show will end at " & FormatDateTime(d, DateFormat.ShortTime) & ".")
Response.Write("<br>The event occur in local time at " & FormatDateTime(o, DateFormat.ShortTime) & ".")
%>

</body>
</html>

This would produce

The Short Time Format

Indeed, a short time value uses the following format: hh:mm AM/PM. To show that format, pass the second argument of the Format() function as t (lowercase). Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim occurrence As Date = #10:35:48 AM#

    Response.Write("The event occurs at " & Format(occurrence, "t"))

    occurrence = #17:29#

    Response.Write("<br>The event occurs at " & Format(occurrence, "t"))
%>

</body>
</html>

This would produce

The Short Time Format

The Long Date Format

To display a time value in long format, pass the second argument of the FormatDateTime() function as LongTime. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
Dim late As String = "12:35 AM"
Dim occurring As String = "#03:18 PM#"

Dim d = CDate(late)
Dim o = CDate(occurring)

Response.Write("The late night TV show will end at " &
		FormatDateTime(d, DateFormat.LongTime) & ".")
Response.Write("<br>The event occur in local time at " &
		FormatDateTime(o, DateFormat.LongTime) & ".")
%>

</body>
</html>

Here is an example of displaying the webpage:

The Long Date Format

Introduction to Date and Time Values

Overview

The values of date and time and usually considered in one unit. To declare a variable for such a value, you can use either the Date data type or the DateTime structure.

If you declare a date/time variable, to initialize it, include the value between # and #. The value can use one of the following formulas:

  • MM-DD-YYYY: The value represents a constant date. The time is set to midnight on that date
  • MM-DD-YYYY hh:mm: The value represents a date without the seconds. The seconds are set to 0
  • MM-DD-YYYY hh:mm:ss: If the hour is between 0 and 11, then it is considered in the morning (AM). Here is an example:
    <%@ Page Language="VB" %>
    
    <!DOCTYPE html>
    <html>
    <head>
    <title>Exercise</title>
    </head>
    <body>
    
    <%
        Dim dteStart As Date = #08-14-2018 08:12:16#
    
        Response.Write("The event starts at " & dteStart)
    %>
    
    </body>
    </html>
    This would produce

    A Combination of Date and Time

  • MM-DD-YYYY hh:mm AM/PM
  • MM-DD-YYYY hh:mm:ss AM/PM

If you declare the variable using the DateTime structure, you can use the following constructor to initialize the variable:

Public Sub New(year As Integer,
	       month As Integer,
	       day As Integer,
	       hour As Integer,
	       minute As Integer,
	       second As Integer)

Here is an example:

<%
    Dim dteStart As New DateTime(2018, 08, 14, 8, 12, 16)

    Response.Write("The event starts at " & dteStart)
%>

The Current Date and Time

To let you get the combination of the current date and the current time, the DateTime structure is equipped with a property named Now:

Public Shared ReadOnly Property Now As Date

The Date Part of a Date/Time Value

To let you extract the date part of a date or of a date/time value, the DateAndTime class is equipped with a property named Date:

Public ReadOnly Property Date As Date

Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim current As Date = Now

    Response.Write("Today and the current time are " & current)
    Response.Write("<br>The date part is " & current.Date)
%>

</body>
</html>

A Date/Time From Parts

One you have a date/time value, you can extract the year, the month, the day, the hour, the minute, and/or the seconds using any of the functions we reviewed already.

Operations on Date/Time Values

Introduction

The concepts of the operations we reviewed for date values are the same for time values. The exception is that, when the dates are considered, the operations performed on time values can affect the dates.

Date/Time Addition

To add a portion to a time value, you use the same DateAdd() function we reviewed for date values. To add a number of hours, pass the first argument as DateInterval.Hour. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim courseStart = #08:15 AM#
    Dim length = 2
    Dim courseEnd = DateAdd(DateInterval.Hour, length, courseStart)

    Response.Write("The course will start at " &
    		   courseStart & " and end at " & courseEnd & ".")
%>

</body>
</html>

This would produce

Time Addition

To add a number of minutes, pass the first argument as DateInterval.Minute, and to add a number of seconds, pass the first argument as DateInterval.Second..

In the same way, you can perform the addition on a value that includes both the date and the time values. If the resulting date occurs after mignight of the first date, the ending date would be different. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim gameStart = #07-31-2016 10:20 PM#
    Dim length = 4
    Dim gameEnd = DateAdd(DateInterval.Hour, length, gameStart)

    Response.Write("The game started on " & 
    		   FormatDateTime(gameStart, DateFormat.ShortDate) & " at " &
                FormatDateTime(gameStart, DateFormat.ShortTime) & " and ended on " &
                   FormatDateTime(gameEnd, DateFormat.ShortDate) & " at " &
                   FormatDateTime(gameEnd, DateFormat.ShortTime) & ".")
%>

</body>
</html>

This would produce

Time Addition

To let you add a number of hours to a date/time value, the DateTime structure is equipped with a method named. Its syntax is:

Public Function AddHours(value As Double) As Date

To add just a number of hours, pass a natural number. To add a number of hours and a fraction of the last hour, pass a decimal number. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim countStart = #08:15 AM#
    Dim countEnd = countStart.AddHours(3.58)

    Response.Write("The count started at " &
    		   countStart & " and ended at " & countEnd & ".")
%>

</body>
</html>

This would produce:

Date-Time Addition

To add a number of minutes to a date/time value, call the DateTime.AddMinutes() method. Its syntax:

<form method="post" action="index.aspx" runat="server">

</form>

Date/Time Subtraction

To find the difference between two time values, you can use the same DateDiff() function we reviewed for date values. To get the difference in hours, pass the first argument as DateInterval.Hour. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim courseStart = #08:15 AM#
    Dim courseEnd = #10:15 AM#
    Dim lapse = DateDiff(DateInterval.Hour, courseStart, courseEnd)

    Response.Write("The course lasted " & lapse & " hours.")
%>

</body>
</html>

This would produce

The Difference Betweeb Two Date-Time Values

To get the difference in a number of minutes, pass the first argument as DateInterval.Minute, and to get the difference in seconds, pass the first argument as DateInterval.Second..

In the same way, you can involve different date/time values in a subtraction. Even if the dates occur on different days, the operation will still work well. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>
<html>
<head>
<title>Exercise</title>
</head>
<body>

<%
    Dim departure = #12-31-2017 10:28 PM#
    Dim arrival = #01-01-2018 06:14 AM#
    Dim hours = DateDiff(DateInterval.Hour, departure, arrival)
    Dim length = DateDiff(DateInterval.Minute, departure, arrival)

    Response.Write("The airplane left the airport on " &
                   FormatDateTime(departure, DateFormat.ShortDate) & " at " &
                   Format(departure, "t") & " and landed on " &
                   FormatDateTime(arrival, DateFormat.ShortDate) & " at " &
                   Format(arrival, "t") & ".")
    Response.Write("<br>The flight lasted " & hours &
    		   " hours and " & (length Mod 60) & " minutes.")
%>

</body>
</html>

This would produce

The Difference Betweeb Two Date-Time Values

 
 
   
 

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