How to resolve the algorithm Luhn test of credit card numbers step by step in the VBA programming language

Published on 12 May 2024 09:40 PM
#Vba

How to resolve the algorithm Luhn test of credit card numbers step by step in the VBA programming language

Table of Contents

Problem Statement

The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits. Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:

For example, if the trial number is 49927398716:

Write a function/method/procedure/subroutine that will validate a number with the Luhn test, and use it to validate the following numbers:

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Luhn test of credit card numbers step by step in the VBA programming language

Source code in the vba programming language

Option Explicit

Sub Main()
  Debug.Print "Number 49927398716 is "; Luhn("49927398716")
  Debug.Print "Number 49927398717 is "; Luhn("49927398717")
  Debug.Print "Number 1234567812345678 is "; Luhn("1234567812345678")
  Debug.Print "Number 1234567812345670 is "; Luhn("1234567812345670")
End Sub
Private Function Luhn(Nb As String) As String
Dim t$, i&, Summ&, s&
    t = StrReverse(Nb)
    For i = 1 To Len(t) Step 2
        Summ = Summ + CInt(Mid(t, i, 1))
    Next i
    For i = 2 To Len(t) Step 2
        s = 2 * (CInt(Mid(t, i, 1)))
        If s >= 10 Then
            Summ = Summ - 9
        End If
        Summ = Summ + s
    Next i
    If Summ Mod 10 = 0 Then
        Luhn = "valid"
    Else
        Luhn = "invalid"
    End If
End Function

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