Question Do While Loop not exiting

[gchq]

Perhaps I'm just tired but...

Have this very simple loop

Dim vFormatText As String = "~"
            Dim ReturnString As String = ""
            Dim vLoop As Integer = 1
            Do While vFormatText <> "/" Or vFormatText <> "" Or vFormatText <> "}" Or vStartIndex >= TextString.Length
                vFormatText = TextString.Substring(vEndIndex + vLoop, 1)
                ReturnString += vFormatText
                vStartIndex = vEndIndex + vLoop
                vLoop += 1
            Loop
            vString.Append(Converter(ReturnString))
            vStartIndex = vEndIndex + vLoop
            vEndIndex = TextString.IndexOf("/", vStartIndex)

And although I can clearly see in debug that vFormatString is passing string.empty ("") the code still keeps looping!

Any ideas?

 

[JohnH]

When either of those expressions are True the loop continues, so it will never end.

[U]vFormatText <> "/"[/U] Or [U]vFormatText <> ""[/U]

when vFormatText is empty string these two expressions evaluate like this, with the combined result equals True. So you have Do While True always.

[U]True[/U] Or [U]False[/U], [B]which equates to True[/B]

Read about it in help: Or Operator (Visual Basic)
resolution:

Do Until vFormatText = "/" OrElse vFormatText = ""...

 

[gchq]

Thanks again John!