Appendix B-1

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Methods and Functions for Working with Dates, Financial Calculations,

Mathematics, and String Operations

Appendix BB

McGraw-Hill © 2006 The McGraw-Hill Companies, Inc. All rights reserved.

Appendix B-3

The DateTime Structure

Use the date functions and the methods of the DateTime structure to: Retrieve the system date Break down a date into component parts Test whether the contents of a field are compatible with

the Date data typeConvert other data types to a date

Appendix B-4

Retrieving the System Date and Time

Use the Now property or the Today property to retrieve the system date and time for the computer’s clockToday retrieves only the date

ExampleDim dateAndTimeDate As DatedateAndTimeDate = NowDim todaysDate As Date = Today

Appendix B-5

Converting Values to a Date Format

To store values in a Date data type convert the value to a Date type

The Date.Parse method and the Convert.ToDateTime method convert a value to Date type Throw an exception if unable to create a valid date from

the argument-use a Try block to make sure to have a valid date value and catch the exception

TryaDate = Date.Parse(Me.dateTextBox.Text)CatchMessageBox.Show("Invalid date.")End Try

Appendix B-6

Finding the Difference Between Dates

Use the Subtract method to find the difference between two Date objectsThe result is in the format of days, hours, minutes, and

secondsThe .NET Framework includes the TimeSpan class

that stores the time differences with the properties that are needed

Dates can be set at a specified time in the future

Appendix B-7

Checking for the Day of the Week

Sometimes a program needs to check for the day of the week for a meeting or an appointment, or rates that differ between weekend and week day

If enteredDate.DayOfWeek = DayOfWeek.Saturday Or _enteredDate.DayOfWeek = DayOfWeek.Sunday ThenweekendCheckBox.Checked = TrueElseweekendCheckBox.Checked = FalseEnd If

Appendix B-8

Financial Functions

VB provides functions for many types of financial and accounting calculationsEliminates the need to know and code the actual

formulasFinancial functions return a value that can be assigned

to a variable, property, or controlEach function needs to have the necessary arguments

Appendix B-9

Mathematical Functions

In Visual Studio.NET, the mathematical functions are included as methods in the System.Math classTo use the methods either import System.Math or refer

to each method with the Math namespace

Appendix B-10

Working with Strings

VB provides many methods for working with text strings

Strings in VS are immutable-once a string is created it cannot be changedStrings seem to be modified but actually a new string is

created when a change is neededStringBuilder class can be used when building or

extensively modifying strings

Appendix B-11

Functions for Checking Validity

The VB namespace also contains functions that can be used to check for validity or type

The preferred technique is to use the methods in the .NET Framework

Appendix B-12

Functions for Formatting Output

VB has some formatting functions which are included in the VB namespace

Using the ToString method, rather then the VB functions is the preferred technique for compatibility among .NET languages