验证信用卡函数（字符串处理）

March 25,2004

验证还取决于信用卡的类型。

'**************************************
' Name: Credit Card Mod 10 Validation
' Description:This function validates if
'    a credit card number "appears" to be val
'    id, depending on the type of card, and a
'    lso performing a Mod 10 check on the num
'    bers.
' By: Lewis Moten
'
'
' Inputs:asCardType - Type of credit car
'    d. (American Express, Discover, Visa, Ma
'    sterCard)
anCardNumber - The number appearing On the card. Dashes and spaces are ok. Numbers are stripped from
the data provided.
'
' Returns:Returns a boolean (true/false)
'    determining if the number appears to be
'    valid or not.
'
'Assumes:The user needs to be able to lo
'    ok through the code and determine wich s
'    trings represent the cards. You can eith
'    er type out the entire card name (i.e. "
'    American Express") or type in just a let
'    ter representing the card name (i.e. "a"
'    )
'
'Side Effects:Just because the function
'    returns that the card is valid, there ar
'    e several other things that are not bein
'    g validated.
Date - make sure the card has Not expired
Active Account - This script does Not communicate With any banks To determine If the account number is
active
Authorization - again, this script does Not communicate With any banks To determine If the card has
authorization to purchase a product.
'
'Warranty:
'code provided by Planet Source Code(tm)
'    (www.Planet-Source-Code.com) 'as is', wi
'    thout warranties as to performance, fitn
'    ess, merchantability,and any other warra
'    nty (whether expressed or implied).
'Terms of Agreement:
'By using this source code, you agree to
'    the following terms...
' 1) You may use this source code in per
'    sonal projects and may compile it into a
'    n .exe/.dll/.ocx and distribute it in bi
'    nary format freely and with no charge.
' 2) You MAY NOT redistribute this sourc
'    e code (for example to a web site) witho
'    ut written permission from the original
'    author.Failure to do so is a violation o
'    f copyright laws.
' 3) You may link to this code from anot
'    her website, provided it is not wrapped
'    in a frame.
' 4) The author of this code may have re
'    tained certain additional copyright righ
'    ts.If so, this is indicated in the autho
'    r's description.
'**************************************

      Function IsCreditCard(ByRef asCardType, ByRef anCardNumber)
         ' Performs a Mod 10 check To make sure the credit card number
         ' appears valid
         ' Developers may use the following numbers as dummy data:
         ' Visa:                   430-00000-00000
         ' American Express:       372-00000-00000
         ' Mastercard:          521-00000-00000
         ' Discover:             620-00000-00000

         Dim lsNumber       ' Credit card number stripped of all spaces, dashes,
etc.
         Dim lsChar          ' an individual character
         Dim lnTotal          ' Sum of all calculations
         Dim lnDigit          ' A digit found within a credit card number
         Dim lnPosition       ' identifies a character position In a String
         Dim lnSum          ' Sum of calculations For a specific Set

         ' Default result is False
         IsCreditCard = False

         ' ====
         ' Strip all characters that are Not numbers.
         ' ====

         ' Loop through Each character inthe card number submited
         For lnPosition = 1 To Len(anCardNumber)
            ' Grab the current character
            lsChar = Mid(anCardNumber, lnPosition, 1)
            ' If the character is a number, append it To our new number
            If IsNumeric(lsChar) Then lsNumber = lsNumber & lsChar

         Next ' lnPosition

         ' ====
         ' The credit card number must be between 13 and 16 digits.
         ' ====
         ' If the length of the number is less Then 13 digits, then Exit the routine
         If Len(lsNumber) < 13 Then Exit Function

         ' If the length of the number is more Then 16 digits, then Exit the routine
         If Len(lsNumber) > 16 Then Exit Function


         ' ====
         ' The credit card number must start with:
         ' 4 For Visa Cards
         ' 37 For American Express Cards
         ' 5 For MasterCards
         ' 6 For Discover Cards
         ' ====

         ' Choose action based on Type of card
         Select Case LCase(asCardType)
            ' VISA
            Case "visa", "v"
                  ' If first digit Not 4, Exit Function
                  If Not Left(lsNumber, 1) = "4" Then Exit Function
            ' American Express
            Case "american express", "americanexpress", "american", "ax", "a"
                  ' If first 2 digits Not 37, Exit Function
                  If Not Left(lsNumber, 2) = "37" Then Exit Function
            ' Mastercard
            Case "mastercard", "master card", "master", "m"
                  ' If first digit Not 5, Exit Function
                  If Not Left(lsNumber, 1) = "5" Then Exit Function
            ' Discover
            Case "discover", "discovercard", "discover card", "d"
                  ' If first digit Not 6, Exit Function
                  If Not Left(lsNumber, 1) = "6" Then Exit Function

            Case Else
         End Select ' LCase(asCardType)

         ' ====
         ' If the credit card number is less Then 16 digits add zeros
         ' To the beginning to make it 16 digits.
         ' ====
         ' Continue Loop While the length of the number is less Then 16 digits
         While Not Len(lsNumber) = 16

            ' Insert 0 To the beginning of the number
            lsNumber = "0" & lsNumber

         Wend ' Not Len(lsNumber) = 16

         ' ====
         ' Multiply Each digit of the credit card number by the corresponding digit of
         ' the mask, and sum the results together.
         ' ====

         ' Loop through Each digit
         For lnPosition = 1 To 16

            ' Parse a digit from a specified position In the number
            lnDigit = Mid(lsNumber, lnPosition, 1)

            ' Determine If we multiply by:
            ' 1 (Even)
            ' 2 (Odd)
            ' based On the position that we are reading the digit from
            lnMultiplier = 1 + (lnPosition Mod 2)

            ' Calculate the sum by multiplying the digit and the Multiplier
            lnSum = lnDigit * lnMultiplier

            ' (Single digits roll over To remain single. We manually have to Do this.)
            ' If the Sum is 10 or more, subtract 9
            If lnSum > 9 Then lnSum = lnSum - 9

            ' Add the sum To the total of all sums
            lnTotal = lnTotal + lnSum

         Next ' lnPosition

         ' ====
         ' Once all the results are summed divide
         ' by 10, If there is no remainder Then the credit card number is valid.
         ' ====
         IsCreditCard = ((lnTotal Mod 10) = 0)

      End Function ' IsCreditCard

ASP精品屋 from http://www.planet-source-code.com/vb/scripts/ShowCode.asp?lngWId=4&txtCodeId=6267