Only numbers, disallow letters -user input

I am writing a console appli开发者_如何学Gocation which requires user input of certain values. I want to disallow any letter input. The console automatically writes "Conversion from string "b" to type 'Integer' is not valid." but I want the console to display my personal message "Not a valid number, please try again." how can I do that?

I've tried many different keywords and phrases but none work. Maybe I'm doing it wrong (not unlikely) or maybe it's just meant for something else. Either way I need help.

To recap: User input in a console that only allows numbers not letters, and will display my message.

I didn't want to post my code since people always pick on it, but here it is. Please note that there MUST be an exception. It is homework and I NEED an exception and this is one way a user can screw up. Please don't tell me not to use an exception.

Module Module1
Sub Main()
    Try
        System.Console.WriteLine("Input up to 10 valid numbers to have them mathematically averaged.")
        For Index = 0 To 9
            Dim Input As IList
            Input = Console.ReadLine()
        Next Index
        If ' here is where I want to add that numbers only Then
            Throw New exception("Not a valid number, please try again.")
        Else
            System.Console.WriteLine("Now averaging numbers...")
            Dim average As Double = (n + n + n + n + n + n + n + n + n + n) / 10
            Console.WriteLine("The average of " & n & "," & n & "," & n & "," & n & "," & n & "," & n & "," & n & "," & n & "," & n & " and " & n & " is " & average & ".", "Calculation")
        End If
    Catch e As Exception
        System.Console.WriteLine(e.Message)
    End Try
End Sub

End Module

---

Dim inputString = Console.ReadLine
If Integer.TryParse(inputString, num) Then
    DoSomething(num)
Else
    Console.WriteLine("Not a valid number, please try again.")
End If

Here's one way to do it, honoring your requirements:

Module Module1
Sub Main()
    System.Console.WriteLine("Input valid numbers seperated by spaces to have them mathematically averaged.")
    Dim inputArray As String() = System.Text.RegularExpressions.Regex.Replace(Console.ReadLine().Trim(), "\s{2,}", " ").Split(New Char() {" "})
    Dim values As New ArrayList
    Dim sum As Integer
    For i As Integer = 0 To inputArray.Length - 1
        Try
            sum = sum + Integer.Parse(inputArray(i), Globalization.NumberStyles.Integer)
            values.Add(inputArray(i))
        Catch ex As Exception
            Console.WriteLine(String.Format("The value ""{0}"" is not a valid number and will be ignored. ExceptionMessage: {1}", inputArray(i), ex.Message))
        End Try
    Next
    Dim average As Decimal = sum / values.Count
    Console.WriteLine(vbCrLf)
    Console.WriteLine(String.Format("The average of ""{0}"" is {1}", Join(values.ToArray, ", "), average))
    Console.WriteLine(vbCrLf)
    Main()
End Sub

End Module

---

Well for starters, the Try - Catch should be inside the input gathering For loop. As your program is written now, as soon as one wrong value is entered execution jumps to the catch and your program ends! If you try casting your input to an decimal you won't need to throw an exception manually, it will be thrown automatically if your input is not an decimal! Try casting the current console input as a decimal and then add that number to your list.

Dim inputNumber as Decimal = CDec(Console.ReadLine())
Input.Add(inputNumber)

Also n will be the same number every time so how you are doing it won't work (look up the basics of how a list works, how to add elements to a list and how to display list elements)