How can I make this VB program recursive?

Question

I need to use recursion in this program for a school project. The program checks if the number inputted is a real number (in this case defined by a number with a decimal with the characters 0-9 (eg 56.7). How would I make the function recursive?

Thanks :-)

Module Real_Numbers

    Sub Main()
        Dim number As String
        Dim check As Boolean
        Console.WriteLine("Enter a number to check if it is a real number:")
        number = Console.ReadLine()
        check = CheckNumber(number)

        If check = True Then
            Console.WriteLine("The number is a real number")
        Else
            Console.WriteLine("The number is not a real number")
        End If
        Console.ReadLine()

    End Sub

    Function CheckNumber(ByVal number As String) As Boolean
        Dim current As Char
        For i As Integer = 0 To number.Length - 1
            current = number.Substring(i, 1)
            If current = "." Then
                ' Do nothing
            Else
                If IsNumeric(current) Then
                    ' Do nothing
                Else
                    Return False
                End If
            End If

        Next

        Return True

    End Function

End Module

Answer 1

Given that this is a homework assignment, I'm not going to write the code out for you. But I will say this -- there are a couple of ways to set this up. One straightforward way would be to pass the string (of the number) to CheckNumber and then check the first character -- if it's numeric, call CheckNumber again with the remainder of the string (everything minus what you just checked). If it's not numeric, return false. You'll need a special case to handle the very last character -- if it's numeric, then return true. If you propagate the boolean response properly, your recursion should unwind itself at the end with the right answer.

Good luck!

Answer 2

You should call the CheckNumber function from within itself, that is a recursion. Learn more about recursion here .