Checking for Digits in a String

Gary has a macro that uses InputBox for the user to input a string. The string can be just about any length. He needs to check the string to make sure it doesn't contain any digits. (Letters are OK, but no digits.) Gary wonders if there an easy way to do this.

There are actually several easy ways to do this. Since Gary is doing his work in a macro, it is probably best to demonstrate the different ways by creating a function that returns False if there are no digits in the string and True if there are digits. Gary could call the function right after getting the user input, and then take some action based on what is returned.

Here is an example of the VBA code you can use when you want to check if entered string contains a digit:

Function CheckInput(sRaw As String) As Boolean
    Dim J As Integer

    CheckInput = False    ' Assume no digits

    For J = 1 To Len(sRaw)
        If IsNumeric(Mid(sRaw, J, 1)) Then
            CheckInput = True
            Exit For
        End If
    Next J
End Sub

This approach is fairly typical of checking—it steps through each character in the string being checked, and if the character is a digit (determined by the IsNumeric function), then the checking is exited and CheckInput returns True.

If the strings being entered are routinely long, then it may be beneficial to turn the checking on its head, in this manner:

Function CheckInput(sRaw As String) As Boolean
    Dim J As Integer

    CheckInput = False    ' Assume no digits

    For J = 0 To 9
        If InStr(sRaw, J) <> 0 Then CheckInput = True
    Next J
End Sub

This approach only requires 10 checks of the string, using the digits 0 through 9. In this case, InStr is used to see if the digit is anywhere in the string being checked. If so, then CheckInput is set to True. Notice, as well, that this approach doesn't use an Exit For statement because ten passes through the string can be executed quickly.

You could make the checking function even shorter by relying on the Like operator, as in the following:

Function CheckInput(sRaw As String) As Boolean
    CheckInput = sRaw Like "*#*"
End Sub

Notice that the check requires only a single line. The Like operator always returns True or False based on a pattern that is compared against, in this case, the sRaw string. The pattern specified for the Like operator is any number of characters followed by a digit followed by any number of characters. Thus, if there is even a single digit in the string, then CheckInput is set to True.

There is another advantage to using the Like function—you can limit what characters will cause the test to fail. Here, for instance, is a variation that only returns True if the string contains the digits 3 through 7.

Function CheckFor37(sRaw As String) As Boolean
    CheckFor37 = sRaw Like "*[3-7]*"
End Sub

This means that the string being checked can contain 0, 1, 2, 8, or 9. It is only 3, 4, 5, 6, and 7 that cause the function to return True.

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