Microsoft Visual Basic 2010 Step by Step eBook

344 Part II Programming Fundamentals

Code = CShort(strCode)

'read encrypted numbers

AllText = My.Computer.FileSystem.ReadAllText(OpenFileDialog1.FileName)

AllText = AllText.Trim

'split numbers in to an array based on space

Numbers = AllText.Split(" ")

'loop through array

For i = 0 To Numbers.Length - 1

Number = CShort(Numbers(i)) 'convert string to number

ch = Chr(Number Xor Code) 'convert with Xor

Decrypt = Decrypt & ch 'and build string

Next

txtNote.Text = Decrypt 'then display converted string

lblNote.Text = OpenFileDialog1.FileName

txtNote.Select(0, 0) 'remove text selection

txtNote.Enabled = True 'allow text cursor

mnuCloseItem.Enabled = True 'enable Close command

mnuOpenItem.Enabled = False 'disable Open command

Catch ex As Exception

MsgBox("An error occurred." & vbCrLf & ex.Message)

End Try

End If

When the user clicks the Open Encrypted File command, this event procedure opens the

encrypted file, prompts the user for an encryption code, and displays the translated file in

the text box object. The ReadAllText method reads the encrypted file. The Split method splits

the numbers as strings into an array and uses the space as a separator. The For loop reads

each string in the array, converts the string to a number, and stores it in the Number short

integer variable. The Number variable is then combined with the Code variable by using the

Xor operator, and the result is converted to a character by using the Chr function. These

characters (stored in the ch variable of type Char) are then concatenated with the Decrypt

string variable, which eventually contains the entire decrypted text file, as shown here:

ch = Chr(Number Xor Code) 'convert with Xor

Decrypt = Decrypt & ch 'and build string

Encryption techniques like this are useful, and they can also be very instructional. Because

encryption relies so much on string-processing techniques, it’s a good way to practice

a fundamental and important Visual Basic programming skill. As you become more

experienced, you can also use the encryption services provided by the .NET Framework to

add much more sophisticated security and cryptography services to your programs. For

an introduction to these topics, search for “Cryptographic Tasks” in the Visual Studio Help

documentation. Because these services rely somewhat on your understanding of classes,

containers, and Internet transactions, I recommend that you finish the chapters in Parts III

and IV of this book before you experiment with them.

Well, now—congratulations! If you’ve worked from Chapters 5 to here, you’ve completed the

programming fundamentals portion of this book, and you are now ready to focus specifically

on creating professional-quality user interfaces in your programs. You have come a long way