I'm doing a VB.net Caesar Cipher - vb.net

Question

Good day,
i'm having trouble of finishing this homework :<
i'm doing a caesar cipher where the user will have a txt file
then the program will find the text file and read what's inside of it
then overwrite the text file
so far i'm able to do the code but i'm getting a
index out of range and nullreference exception
here's my code
Imports System.IO
Public Class main_form
Dim x, y, z, str_len As Integer 'where x is a counter for the array
Dim loc, read(5), write(), str_1, str_2, aa As String
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
End Sub
Private Sub brw_btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles brw_btn.Click
TextBox1.Clear()
OFD1.ShowDialog()
TextBox1.Text = OFD1.FileName
loc = OFD1.FileName
read = File.ReadAllLines(OFD1.FileName)
End Sub
Private Sub enc_btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles enc_btn.Click
'Formula of Caesar's Cipher
z = 1
x = 0
If read(x) <> "" Then
While read(x) <> ""
str_2 = ""
str_1 = read(x)
str_len = Len(str_1)
MessageBox.Show(str_2)
For i As Integer = 0 To str_len - 1
y = Asc(Mid(str_1, i + 1, i + 2))
y = y + Val(TextBox2.Text)
str_2 = str_2 + Chr(y)
MessageBox.Show(str_2)
Next
MessageBox.Show(str_2)
write(x) = str_2
File.AppendAllLines(OFD1.FileName, write(x))
x += 1
End While
Else
End If
End Sub
End Class
Thanks!

Answer 1

Of course you are getting out of range exception because :
While read(x) <> ""
...
...
x += 1 'if x goes out of range the next loop in while will access read(x <-out of range)
End While
You have to insert
While read(x) <> ""
...
...
x += 1
If x >= read.Length
Exit While
End If
End While
Also:
Dim write() as String
...
write(x) = str_2 '<-write is used un initialized, null reference exception
Change write() to write or:
Private Sub enc_btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles enc_btn.Click
ReDim write(read.Length) '<---
z = 1
x = 0
If read(x) <> "" Then
...
...
Valter