Microsoft Visual Basic 2010 Step by Step eBook

Chapter 13 Exploring Text Files and String Processing 347

To Do This

Convert text

characters to ASCII

codes

Use the Asc function. For example:

Dim Code As Short

Code = Asc("A") 'Code equals 65

Convert ASCII codes

to text characters

Use the Chr function. For example:

Dim Letter As Char

Letter = Chr(65) 'Letter equals "A"

Encrypt text Use the Xor operator and a user-defined encryption code. For example,

this code block uses Xor and a user code to encrypt the text in the txtNote

text box and to save it in the encrypt .txt file as a series of numbers:

strCode = InputBox("Enter Encryption Code")

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)

StreamToWrite.Write(Asc(letter) Xor Code)

StreamToWrite.Write(" ")

Next

StreamToWrite.Close()

Decrypt text Request the code that the user chose to encrypt the text, and use Xor to

decrypt the text. For example, this code block uses Xor and a user code to

reverse the encryption created in the preceding example:

strCode = InputBox("Enter Encryption Code")

Code = CShort(strCode)

AllText = My.Computer.FileSystem.ReadAllText( _

OpenFileDialog1.FileName)

Numbers = AllText.Split(" ")

For i = 0 To Numbers.Length – 1

Number = CShort(Numbers(i))

ch = Chr(Number Xor Code)

Decrypt = Decrypt & ch

Next

txtNote.Text = Decrypt