How can I compare whether a data type is, or is not, equal to a specific data type?

Question

Dim firstName As String

Console.Write("Please enter your first name: ")
firstName = Console.ReadLine() 'Accepts user's first name

Now how would I compare the data type of "firstName" to another data type, for example integer? That way, I could use an If statement to compare the data types and output an error message if the data the user inputted is erroneous.

I tried this:

Dim firstName As String

Console.Write("Please enter your first name: ")
firstName = Console.ReadLine()

If firstName IsNot GetType(String) Then
    Console.Write("Error, please try again: ")
End If

This did not work because every time, the statement would equal false and so the error message would never be outputted regardless of the data type inputted.

Answer 1

If you want to check the string for letters do something like that:

Function CheckForAlphaCharacters(ByVal StringToCheck As String)
    For i = 0 To StringToCheck.Length - 1
        If Not Char.IsLetter(StringToCheck.Chars(i)) Then
            Return False
        End If
    Next

    Return True 'Return true if all elements are characters
End Function

You can also check for whitespaces in the string:

Function CheckForAlphaCharacters(ByVal StringToCheck As String)
    For i = 0 To StringToCheck.Length - 1
        If Not Char.IsLetter(StringToCheck.Chars(i)) And Not Char.IsWhiteSpace(StringToCheck.Chars(i)) Then
            Return False
        End If
    Next

    Return True 'Return true if all elements are characters or whitespaces
End Function