How Do I pass the result of a variable in this vb app?

Question

I have written the piece of code below to calculate factorials of numbers more than or equal to 1.

Public Class FactorialApp

    Private Function FactorialChecker(myNumber As Integer)
        myNumber = Val(FactorialTextBox.Text)
        If myNumber < 1 Then
            FactorialChecker = 1

        Else
            FactorialChecker = myNumber * FactorialChecker(myNumber - 1)
        End If
    End Function

    Public Sub ResultButton_Click(sender As Object, e As EventArgs) Handles ResultButton.Click

    End Sub

End Class

I want to have a message box in a button_click event that says something like The factorial of 5 is 120 when clicked where 5 is supposed to be myNumber and 120 the FactorialChecker() function, but I have no idea how to return values in VB's MsgBox command, I'm only used to C#'s .

I tried the code snippet

    MsgBox("The Factorial of  + myNumber "is" + FactorialChecker() "") 

But I got stomped by syntax errors in visual studio and also an error that my myNumber variable wasn't declared in the program. What can I do to fix these errors please?

Answer 1

Like this:

MsgBox("The Factorial of " + myNumber + " is " + FactorialChecker()) 

You just didn't close your quotes for the first part of the string so they're unbalanced, thus your compiler errors. Also, I added some spaced because I assume you'll want them.

Note that in VB.NET, using MessageBox.Show is preferable to the old VB6-style MsgBox function. Also, in VB, the & operator is typically recommended over the + operator for string concatenations, since the + operator can have some unexpected results when you have Option Strict Off. So, this would be the better way to do that:

MessageBox.Show("The Factorial of " & myNumber & " is " & FactorialChecker()) 

Answer 2

myNumber is declared inside the FactorialChecker function. If you try to access it outside that function it won't exist. You might need to make it a property of the class.

Answer 3

For a first attempt, move myNumber = Val(FactorialTextBox.Text) into your button Click handler. If you reload it every time your FactorialChecker function is called, then your recursion won't work the way you want it to.

Also, you're not declaring it or specifying a type, so you may want to change that line to Dim myNumber As Double = Val(FactorialTextBox.Text). Then below it, add the MessageBox.Show call, as others have said.

Val() may not be a good choice, since it returns a Double, and the factorial function is defined only for non-negative integers. You probably actually want myNumber to be an Integer (or a Long, or something else, depending on the range you need). You could then replace Val() with CInt(), or Integer.Parse, or Integer.TryParse, and add error-checking to make sure the value is non-negative.Integer.TryParse, and add error checking to make sure the value is non-negative.