Page 141 - Excel Progamming Weekend Crash Course

h540629 ch09.qxd 9/2/03 9:34 AM Page 116

116 Saturday Morning

Listing 9-1 Determining if a string represents a number

Public Function IsNumber(s As String) As Boolean

‘ Returns True if the argument is a number
‘ containing only the digits 0-9.
‘ Returns False otherwise.
Dim i As Integer
Dim buf As String * 1

IsNumber = True

‘ Return False if an empty string was passed.
If Len(s) = 0 Then
IsNumber = False
Exit Function
End If
‘ Loop thru all characters in s.
For i = 1 To Len(s)
‘ Extract the ith character.
buf = Mid(s, i, 1)
If Asc(buf) < 48 Or Asc(buf) > 57 Then
IsNumber = False
Exit For
End If
Next i

End Function
Public Sub TestIsNumber()

Dim str As String
Dim InputOK As Boolean

‘ The default for Boolean values is False,
‘ but it never hurts to explicitly initialize
‘ the value in code.
InputOK = False
Do
str = InputBox(“Please enter an integer number:”)
InputOK = IsNumber(str)
Loop Until InputOK

MsgBox “Thank you!”

End Sub