ChallengingProgramming. ( 2 )

Programming ( Mathematical )  Practice for Fun:

 Question:

       An ISBN (International Standard Book Number) is a ten digit code which uniquely identifies a book.   The first nine digits represent the book and the last digit is used to make sure the ISBN is correct.  To verify an ISBN you calculate 10 times the first digit, plus 9 times the second digit, plus 8 times the third ... all the way until you add 1 times the last digit.  If the final number leaves no remainder when divided by 11 the code is a valid ISBN. 

                                       

               For example: 0201103311 is a valid ISBN,  since

        10*0 + 9*2 + 8*0 + 7*1 + 6*1 + 5*0 + 4*3 + 3*3 + 2*1 + 1*1 = 55. 

                       

    Each of the first nine digits can take a value between 0 and 9.  Sometimes it is necessary to make the last digit equal to ten; this is done by writing the last digit as X.  For example: 156881111X.           

  Write a program that reads in a valid ISBN with a single missing digit, marked with a “ ? “ , and outputs the correct value for the missing digit.

  

                                                                   

                    Sample Input         Sample Output             

               ISBN: 15688?111X         Missing Digit: 1

                                                                            

Solution:

 Visual Basic

Module Module1

    Sub Main()

        Dim ISBNcode As String

        Dim total1, temp, total2 As Integer

        Dim counter1 As Integer = 1

        Console.Write("ISBN: ")

        ISBNcode = Console.ReadLine()

        Dim digit(10) As String

        Dim counter As Integer

        For counter = 1 To Len(ISBNcode)

            digit(counter) = Mid(ISBNcode, counter, 1)

        Next

        If digit(10) = "X" Then digit(10) = "10"

        For counter = 10 To 1 Step -1

            If digit(counter1) = "?" Then

                temp = counter

                counter1 = counter1 + 1

            Else

                total1 = total1 + Val(digit(counter1)) * counter

                counter1 = counter1 + 1

            End If

        Next

        For counter = 0 To 10

            total2 = temp * counter + total1

            If total2 Mod 11 = 0 And counter = 10 Then

                Console.WriteLine("Missing Digit: X")

            Else

                If total2 Mod 11 = 0 Then Console.WriteLine("Missing Digit: " & counter)

            End If

        Next

        Console.ReadKey()

    End Sub

End Module