Increment character in a string - vb.net

Question

I have a 2 character string composed only of the 26 capital alphabet letters, 'A' through 'Z'.
We have a way of knowing the "highest" used value (e..g "IJ" in {"AB", "AC", "DD", "IH", "IJ"}). We'd like to get the "next" value ("IK" if "IJ" is the "highest").
Function GetNextValue(input As String) As String
Dim first = input(0)
Dim last = input(1)
If last = "Z"c Then
If first = "Z"c Then Return Nothing
last = "A"c
first++
Else
last++
EndIf
Return first & last
End Function
Obviously char++ is not valid syntax in VB.NET. C# apparently allows you to do this. Is there something shorter less ugly than this that'd increment a letter? (Note: Option Strict is on)
CChar(CInt(char)+1).ToString
Edit: As noted in comment/answers, the above line won't even compile. You can't convert from Char -> Integer at all in VB.NET.

Answer 1

The tidiest so far is simply:
Dim a As Char = "a"
a = Chr(Asc(a) + 1)
This still needs handling for the "z" boundary condition though, depending on what behaviour you require.
Interestingly, converting char++ through developerfusion suggests that char += 1 should work. It doesn't. (VB.Net doesn't appear to implicitly convert from char to int16 as C# does).
To make things really nice you can do the increment in an Extension by passing the char byref. This now includes some validation and also a reset back to a:
<Extension>
Public Sub Inc(ByRef c As Char)
'Remember if input is uppercase for later
Dim isUpper = Char.IsUpper(c)
'Work in lower case for ease
c = Char.ToLower(c)
'Check input range
If c < "a" Or c > "z" Then Throw New ArgumentOutOfRangeException
'Do the increment
c = Chr(Asc(c) + 1)
'Check not left alphabet
If c > "z" Then c = "a"
'Check if input was upper case
If isUpper Then c = Char.ToUpper(c)
End Sub
Then you just need to call:
Dim a As Char = "a"
a.Inc() 'a is now = "b"

Answer 2

My answer will support up to 10 characters, but can easily support more.
Private Sub Test
MsgBox(ConvertBase10ToBase26(ConvertBase26ToBase10("AA") + 1))
End Sub
Public Function ConvertBase10ToBase26(ToConvert As Integer) As String
Dim pos As Integer = 0
ConvertBase10ToBase26 = ""
For pos = 10 To 0 Step -1
If ToConvert >= (26 ^ pos) Then
ConvertBase10ToBase26 += Chr((ToConvert \ (26 ^ pos)) + 64)
ToConvert -= (26 ^ pos)
End If
Next
End Function
Public Function ConvertBase26ToBase10(ToConvert As String) As Integer
Dim pos As Integer = 0
ConvertBase26ToBase10 = 0
For pos = 0 To ToConvert.Length - 1
ConvertBase26ToBase10 += (Asc(ToConvert.Substring(pos, 1)) - 64) * (26 ^ pos)
Next
End Function

Answer 3

Unfortunately, there's no easy way -- even CChar(CInt(char)+1).ToString doesn't work. It's even uglier:
CChar(Char.ConvertFromUtf32(Char.ConvertToUtf32(myCharacter, 0) + 1))
but of course you could always put that in a function with a short name or, like Jon E. pointed out, an extension method.

Answer 4

Try this
Private Function IncBy1(input As String) As String
Static ltrs As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
Dim first As Integer = ltrs.IndexOf(input(0))
Dim last As Integer = ltrs.IndexOf(input(1))
last += 1
If last = ltrs.Length Then
last = 0
first += 1
End If
If first = ltrs.Length Then Return Nothing
Return ltrs(first) & ltrs(last)
End Function
This DOES assume that the code is only two chars, and are A-Z only.

Answer 5

Dim N as String = ""
Dim chArray As Char = Convert.ToChar(N)
Dim a As String = CChar(Char.ConvertFromUtf32(Char.ConvertToUtf32(chArray, 0) + 1))