How can I check if a string only contains letters?

Question

I\'m using a function that allows me to review a string of text and evaluate if it is composed of letters. It is housed in a module called \"General\". The general module

Answer 1

Try this for IsAlpha

Public Function IsAlpha(strValue As String) As Boolean
Dim intPos As Integer

    For intPos = 1 To Len(strValue)
        Select Case Asc(Mid(strValue, intPos, 1))
            Case 65 To 90, 97 To 122
                IsAlpha = True
            Case Else
                IsAlpha = False
                Exit For
        End Select
    Next
End Function

Answer 2

The most direct, concise, and performant way to check if a string contains only alpha characters is with this function:

Function IsAlpha(s) As Boolean
    IsAlpha = Len(s) And Not s Like "*[!a-zA-Z]*"
End Function

Answer 3

Left(Me.TxtDxCode.Text, 2) returns the first two characters of the string. So, if Me.TxtDxCode.Text was 7ZABC, this expression would return "7Z". This would cause the IsAlpha test to fail.

As you want to examine just the 2nd character, use Mid$ instead:

If IsAlpha(Mid$(Me.TxtDxCode.Text, 2, 1)) Then

This will return "Z" and the IsAlpha test should now succeed

(The string versions Left$, Mid$ etc are slightly faster than the variant versions Left, Mid etc - see here)

Answer 4

Why don't you use regular expressions instead? Then there's no loops involved:

Public Function IsAlpha(strValue As String) As Boolean
    IsAlpha = strValue Like WorksheetFunction.Rept("[a-zA-Z]", Len(strValue))
End Function

Also, when you create a User-Defined Function (UDF) you need to ensure that the return value is assigned to the name of the actual function, in this case IsAlpha - not IsLetter otherwise the value will never be passed back.