Check String for identical Digits - vb.net

Question

I'm asking my users to enter a 4 - 6 digit numberic PIN. And I'd like to make sure users can't enter 0000 or 11111 or 333333. How can I check a string for 4 consecutive identical digits? I'm using vb.net.

Answer 1

See code snippet below:
Sub Main()
Dim a As String = "001111"
Dim b As String = "1123134"
Dim c As String = "1111"
Console.WriteLine(CheckConsecutiveChars(a, 4)) 'True => Invalid Pin
Console.WriteLine(CheckConsecutiveChars(b, 4)) 'False => Valid Pin
Console.WriteLine(CheckConsecutiveChars(c, 4)) 'True => Invalid Pin
Console.ReadLine()
End Sub
'maxnumber = maximum number of identical consecutive characters in a string
Public Function CheckConsecutiveChars(ByVal j As String, ByVal maxNumber As Integer) As Boolean
Dim index As Integer = 0
While ((index + maxNumber) <= j.Length)
If (j.Substring(index, maxNumber).Distinct.Count = 1) Then
Return True
End If
index = index + 1
End While
Return False
End Function
The method String.Distinct.Count() counts the number of distinct characters in a string. You cast your digit to a String and test for the number of different characters. If the result is 1 then the user has entered the same number.
Note: If you're using the Substring, you must check the length of the string first (is it long enough) to avoid exceptions.

Answer 2

This answer is similar to the accepted answer, but does not create lots of temporary strings in memory.
'maxnumber = maximum number of identical consecutive characters in a string
Public Function HasConsecutiveChars(ByVal j As String, ByVal maxNumber As Integer) As Boolean
Dim result As Boolean = False
Dim consecutiveChars As Integer = 1
Dim prevChar As Char = "x"c
For Each c in j
If c = prevChar Then
consecutiveChars += 1
If consecutiveChars >= maxNumber Then
result = True
Exit For
End If
Else
consecutiveChars = 1
End If
prevChar = c
Next
Return result
End Function