VB.NET Increment string

Hi all, I am using this code to increment a string. The string can contain letters, numbers and some special characters and usually works pretty well. Since its difficult to try out many combinations, the one I am having trouble with now is a four digit string like "3067" that should go to "3068" but changes it to "368" unless I have a special character in front of it. I'm not sure if what I am using is the correct code for incrementing various strings. Thanks for any suggestions on this.

Code:

---

  Public Function IncrementString(ByVal Sender As String) As String

        Dim Index As Integer

        For Item As Integer = Sender.Length - 1 To 0 Step -1
            Select Case Sender.Substring(Item, 1)
                Case "0" To "9"

                Case Else
                    Index = Item
                    Exit For
            End Select
        Next

        If Index = Sender.Length - 1 Then
            Return Sender & "1" '  Optionally throw an exception ?

        Else
            Dim x As Integer = Index + 1
            Dim value As Integer = Integer.Parse(Sender.Substring(x)) + 1
            Return Sender.Substring(0, x) & value.ToString()
        End If

    End Function

---

You posted this exact same code almost 1 year ago and I and others pointed out many pitfalls and gotcha's with your current approach with regard to many potential formats of serial strings. At that time I also gave you a suggested simple one-line code change that *may* solve the issue for you.

https://www.vbforums.com/showthread....ric&highlight=

Quote:

---

Originally Posted by mikeg71

I'm not sure if what I am using is the correct code for incrementing various strings.

---

That statement makes programmers shudder, because "for incrementing various strings" is completely meaningless without context. The last time you posted about this, you at least included examples of what types of Strings you are passing in to the Function, and what you want to come back out of the Function.

But the answer is no, it is not the correct code for your needs, because if it was, it would be producing the output you desire.

What are the rules for the formation of these strings and for each variant examples of the next number?

'optionbase1' - I completely overlooked my last post from a year ago. That is my fault 100%. See some of my examples below, but like I mentioned, this does work "most" of the time. But one sneaks in that doesn't seem to handle properly and I just want to understand more on how to deal with it.

'dbasnett' - To answer yours, there really isn't any rules that exist for this as there is the possibility of having many variations. These are serial numbers that get assigned for various products and I don't get the chance to see them in advance. But they are typically in the form of and should increment to:

Code:

---

F-2389 -to- F-2390
F2891 -to- F2892
8057 -to- 8058
8057-D234 -to- 8057-D235

---

Quote:

---

Originally Posted by mikeg71

'optionbase1' - I completely overlooked my last post from a year ago. That is my fault 100%. See some of my examples below, but like I mentioned, this does work "most" of the time. But one sneaks in that doesn't seem to handle properly and I just want to understand more on how to deal with it.

---

I explained exactly why this is happening in my first reply to you last year, and as I mentioned above, I offered a very simple change to 1 line of your code that might fix the issue. Did you try it?

Try this, just some minor tweaks.

Code:

---

    Public Function IncrementString(StringToIncrement As String) As String
        Const nums As String = "0123456789"
        Dim Index As Integer
        For Index = StringToIncrement.Length - 1 To 0 Step -1
            If Not nums.Contains(StringToIncrement.Substring(Index, 1)) Then
                Exit For
            End If
        Next
        Index += 1
        If Index >= StringToIncrement.Length Then
            Return StringToIncrement & "1" '  Optionally throw an exception ?
        Else
            Dim length As Integer = StringToIncrement.Length - Index
            Dim value As Integer = Integer.Parse(StringToIncrement.Substring(Index, length)) + 1
            Return StringToIncrement.Substring(0, Index) & value.ToString()
        End If

    End Function

---

Try the following

Code:

---

Imports System.Runtime.CompilerServices

Public Class Form1
    Private Sub IncrementButton_Click(sender As Object, e As EventArgs) Handles IncrementButton.Click
        Dim values As New List(Of String) From {"F-2389", "F2891", "8057", "8057-D234", "X1 X1"}

        For Each value As String In values
            Debug.WriteLine($"{value} to {value.Increment}")
        Next

    End Sub
End Class

Public Module Helpers
    <Extension>
    Public Function Increment(value As String) As String
        If String.IsNullOrWhiteSpace(value) Then
            Return ""
        End If

        Dim characterArray = value.ToCharArray()

        For characterIndex = characterArray.Length - 1 To 0 Step -1
            Dim characterValue = Convert.ToInt32(characterArray(characterIndex))

            If characterValue <> 57 AndAlso characterValue <> 90 AndAlso characterValue <> 122 Then
                characterArray(characterIndex) = ChrW(AscW(characterArray(characterIndex)) + 1)

                For resetIndex As Integer = characterIndex + 1 To characterArray.Length - 1
                    characterValue = Convert.ToInt32(characterArray(resetIndex))
                    If characterValue >= 65 AndAlso characterValue <= 90 Then
                        characterArray(resetIndex) = "A"c
                    ElseIf characterValue >= 97 AndAlso characterValue <= 122 Then
                        characterArray(resetIndex) = "a"c
                    ElseIf characterValue >= 48 AndAlso characterValue <= 57 Then
                        characterArray(resetIndex) = "0"c
                    End If
                Next

                Return New String(characterArray)

            End If
        Next

        'If we got through the Character Loop and were not able to
        'increment anything, we return a NULL string.
        Return Nothing
    End Function

End Module

---

C# version

Code:

---

public static class Helpers
{
    public static string Increment(this string sender)
    {
        string value = Regex.Match(sender, "[0-9]+$").Value;
        return sender[..^value.Length] + (long.Parse(value) + 1).ToString().PadLeft(value.Length, '0');
    }
}

---

@OptionBase1 - I found that I had used your change in another small application and so far it seems to be working. Without investigating it further, I had assumed I made the change to my current project. I will continue trying this out and see how it comes along. Thanks a lot for your time and catching this from a year ago.

Quote:

---

Originally Posted by dbasnett

Try this, just some minor tweaks.

Code:

---

    Public Function IncrementString(StringToIncrement As String) As String
        Const nums As String = "0123456789"
        Dim Index As Integer
        For Index = StringToIncrement.Length - 1 To 0 Step -1
            If Not nums.Contains(StringToIncrement.Substring(Index, 1)) Then
                Exit For
            End If
        Next
        Index += 1
        If Index >= StringToIncrement.Length Then
            Return StringToIncrement & "1" '  Optionally throw an exception ?
        Else
            Dim length As Integer = StringToIncrement.Length - Index
            Dim value As Integer = Integer.Parse(StringToIncrement.Substring(Index, length)) + 1
            Return StringToIncrement.Substring(0, Index) & value.ToString()
        End If

    End Function

---

---

dbasnett - This also seems to be working. I am going to continue on with these suggestions. Thanks a bunch for the help and your time.