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Credit Card Checksum Checker

Checks to see if a Credit Card Number is valid by performing the LUHN-10 check on it.

Inputs
CCNum as String

Returns
True if Valid, False if Invalid

Side Effects
May cause skin irritation

API Declarations



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(106(106 Vote))

Public Function IsValidCCNum(CCNum As String) As Boolean
  Dim i As Integer
  Dim total As Integer
  Dim TempMultiplier As String
  For i = Len(CCNum) To 2 Step -2
    total = total + CInt(Mid$(CCNum, i, 1))
    TempMultiplier = CStr((Mid$(CCNum, i - 1, 1)) * 2)
    total = total + CInt(Left$(TempMultiplier, 1))
    If Len(TempMultiplier) > 1 Then total = total + CInt(Right$(TempMultiplier, 1))
  Next
  If Len(CCNum) Mod 2 = 1 Then total = total + CInt(Left$(CCNum, 1))
  If total Mod 10 = 0 Then
    IsValidCCNum = True
  Else
    IsValidCCNum = False
  End If
End Function