Make sure that the maximum index of a list is less than its size

[Hb_Kai]

I'm only learning right now and what I'm trying to do is to test a TextBox text to see if the user has entered a valid email address (if contains @ symbol)

So far I've got things right, but somehow I'm getting the error message "Make sure that the maximum index of a list is less than its size" and I don't know where I've gone wrong.

This is the code I'm using for this...

        Dim email As String
        Dim counter As Integer


        email = Trim(TextBox2.Text)

        For i = 0 To email.Length
            If email.Chars(i) = "@" Then    !The error highlights and points to this line!
                counter = counter = 1
            End If
        Next i

        If counter = 1 Then
            MsgBox("Thank you for your email address")
        ElseIf counter > 1 Then
            MsgBox("Enter a valid email addres")
        End If

Where am I going wrong?

 

[jmcilhinney]

Look at this line:

For i = 0 To email.Length

Let's assume that there are 10 characters in your string. That loop is going to loop from 0 to 10. That's 11 iterations, which is a problem if there are only 10 characters. If the first index is 0 rather than 1, what does that mean for the last index?

 

[Hb_Kai]

Doesn't the count start at 0? If it does, would it mean that the count can only fit the first character in and can't loop the rest of the email address?

 

[MattP]

10 elements starting at 1

1 2 3 4 5 6 7 8 9 10

10 elements starting at 0

0 1 2 3 4 5 6 7 8 9

So if your length is 10 and you're starting at 0...

For i = 0 To email.Length - 1

Jmcilhinney was trying to get you to come to this conclusion on your own.

 

[Hb_Kai]

I thought that already but wasn't sure. Think I worded the reply wrong too. :S

I tried using that in the code anyway but nothing happened when I clicked the button. :S

 

[cjard]

You know, youre writing an awful lot of code to achieve something Microsoft already did:

If txtEmailAddress.Text.Contains("@") Then
  'thanks for your email address
Else
  'please provide an email address
End If

ps; when you drop a textbox on a form, and the forms designer names it TextBox2.. youre supposed to rename it to something meaningful

 

[JuggaloBrotha]

Instead of just checking for an '@' in the email string, I'd use Regex to validate it.

 

[cjard]

Instead of just checking for an '@' in the email string, I'd use Regex to validate it.

But what regex? Be careful..
How to Find or Validate an Email Address

 

[JohnH]

MailAddress class (System.Net.Mail) can also be used for simple validation of the address string, slightly better than checking for a "@".

 

[JuggaloBrotha]

But what regex? Be careful..
How to Find or Validate an Email Address

It's more lenient about it but I use this pattern: "\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" without the quotes