Microsoft Visual Basic 2010 Step by Step eBook

342 Part II Programming Fundamentals

The program opens the file and restores the text by using the Xor operator and the

encryption code you specified.

10. On the File menu, click the Exit command to end the program.

Examining the Encryption Program Code

The Xor operator is used in both the mnuSaveAsItem_Click and the mnuOpenItem_Click event

procedures. By now, these generic menu processing routines will be fairly familiar to you. The

mnuSaveAsItem_Click event procedure consists of these program statements (noteworthy

lines in bold):

Dim letter As Char

Dim strCode As String

Dim i, charsInFile, Code As Short

Dim StreamToWrite As StreamWriter = Nothing

SaveFileDialog1.Filter = "Text files (*.txt)|*.txt"

If SaveFileDialog1.ShowDialog() = DialogResult.OK Then

Try

strCode = InputBox("Enter Encryption Code")

If strCode = "" Then Exit Sub 'if cancel clicked

'save text with encryption scheme

Code = CShort(strCode)

charsInFile = txtNote.Text.Length

StreamToWrite = My.Computer.FileSystem.OpenTextFileWriter( _

SaveFileDialog1.FileName, False)

For i = 0 To charsInFile - 1

letter = txtNote.Text.Substring(i, 1)

'convert to number w/ Asc, then use Xor to encrypt

StreamToWrite.Write(Asc(letter) Xor Code) 'and save in file

'separate numbers with a space

StreamToWrite.Write(" ")

Next

mnuCloseItem.Enabled = True

Catch ex As Exception