Option Strict On
Option Explicit On
Public Class frmMain
    'Warning!  This program does no check for non-numeric inputs.  Try fixing this at home
    '(fairly easy)
    Private Sub btnAverage_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAverage.Click
        Dim num As Double = 0
        Dim count As Integer = 0
        Dim sum As Double = 0
        'Prompt for the input dialog box
        Dim prompt As String = "Enter a nonnegative number.  " &
                               "Enter -1 to terminate entering numbers."
        'Asks the user for the first number
        num = CDbl(InputBox(prompt, "Enter a Number"))
        'While the user has not entered negative 1
        Do While num <> -1
            'adds 1 to the counter variable
            count += 1
            'Adds the number to the total sum
            sum += num
            'Takes in the user's input again
            num = CDbl(InputBox(prompt, "Enter a number"))
        Loop

        'If the user has entered in no numbers, say so, otherwise output the average
        If count > 0 Then
            MessageBox.Show("Average: " & CStr(sum / count), "Average")
        Else
            MessageBox.Show("No numbers were entered.", "No Numbers Were Entered")
        End If
    End Sub
End Class