increment alphanumeric string where alphabet position in a string is keeps changing - vb.net

Question

I need to save Multiple(about 20-25) serial number of the specimen in my application. Sometimes serial number will be alphanumeric but will be sequential. I need a way out to increment alphanumeric serial numbers based on the first serial number entered.
My main problem is alphabet position and alphabet count keeps changing. Example : 10MG2015 20562MG0 MGX02526 etc etc
I tried but mine works when Alphabet are in starting position and when there are known number of alphabets. Here is my try
Dim intValue as integer
Dim serialno as string
Dim serialno1 as string
For i =0 to 20
Serialno1 = serialno.Substring(3)
Int32.TryParse(Serialno1, intValue)
intValue = intValue + 1
checkedox1.items.add(serialno.Substring(0,3) + intValue.ToString("D3"))
NEXT
Any help is highly appreciated. Thanks in advance
edit 1
Clarity : I want to increment alphanumeric string. Example : If first entered one is 10MG2015 then I should increment to 10MG2016, 10MG2017, 10MG2018, 10MG2019 and so on... For 20562MG0 it will be 20562MG1, 20562MG2 20562MG3 and so on...

Answer 1

Function FindSequenceNumber(SerialNumber As String) As Integer
'Look for at least four digits in a row, and capture all the digits
Dim sequenceExpr As New Regex("([0-9]{4,11})")
Dim result As Integer = -1
Dim m As Match = sequenceExpr.Match(SerialNumber)
If m.Success AndAlso Integer.TryParse(m.Groups(1).Value, result) Then
Return result
Else
'Throw exception, return -1, etc
End If
End Function
See it here:
https://dotnetfiddle.net/gO2nue
Note: the integer type doesn't preserve leading zeros. You may find it better to return a tuple with either the length of the original string, so you can pad zeros to the left if needed to match the original formatting.
Or maybe this:
Function IncrementSerial(SerialNumber As String) As String
'Look for at least four digits in a row, and capture all the digits
Dim sequenceExpr As New Regex("([0-9]{4,11})")
Dim m As Match = sequenceExpr.Match(SerialNumber)
If Not m.Success Then Throw New Exception("No sequence number found")
Dim c = m.Groups(1).Captures(0)
Dim seq = (Integer.Parse(c.Value) + 1).ToString()
If seq.Length < c.Value.Length Then
seq = seq.PadLeft(c.Value.Length, "0"c)
End If
Dim result As String = ""
If c.Index > 0 Then result & = SerialNumber.Substring(0, c.Index)
result &= seq
If c.Index + seq.Length < SerialNumber.Length Then result &= SerialNumber.SubString(c.Index + seq.Length)
Return result
End Function