VBA Inputbox to Prevent Decimals - excel

Question

I am trying to develop a tool that will help standardize a description catalog of products. I want to have an input box prompt a user to enter a size. I want to encourage size entries like "5-1/2" and prevent users from entering "5.5". Ideally, if the size was entered with a decimal and not a dash with a fraction, I want a message box to pop up saying they can not do that. It would then need to re-show the input box.
Here is what I have -
Private Sub CS_Other_Click()
Unload Me
Sheets("Fill In").Activate
Worksheets("Fill In").Range("C2").NumberFormat = "#"
Dim other_casing_size As Variant
other_casing_size = InputBox("Fill in the casing size. Syntax MUST be in the form of X-X/X", "New Casing Size")
Range("C2") = other_casing_size
I just dont know the code to prevent an entry with decimals. Even better, if i knew how to code an exact syntax to include or exclude anything I wanted that would be perfect.
Thanks

Answer 1

A while loop, which checks the input string for a dot or comma would work quite ok, I guess:
Sub TestMe()
Dim inputString As String
Dim inputNumeric As Boolean
inputString = InputBox("Please, enter a number!")
inputNumeric = isNumeric(Evaluate(inputString))
Do While InStr(1, inputString, ".") Or _
InStr(1, inputString, ",") Or _
Not inputNumeric
If Not CBool(inputNumeric) Then
MsgBox "You tried to cancel or entered empty value!"
Exit Do
End If
MsgBox "Please, do not write dot or comma!"
inputString = InputBox("Please, enter a number!")
inputNumeric = isNumeric(Evaluate(inputString))
Loop
End Sub
The isNumeric() checks the input for being able to be converted to numeric. Thus 5-1/2 should be ok.
Concerning cancellation or entering empty value from the InputBox() - it really depends on the business logic of the "app", but in the case above - there is a msgbox and it exits the loop.

Answer 2

Write a separate function responsible for that prompt, and use it e.g. like this:
Dim casingSize As String
If GetCasingSize(casingSize) Then
ActiveSheet.Range("C2").Value = casingSize
End If
The function needs to return a Boolean for this to work - it returns True if the input is valid, False if there's no valid input to work with (e.g. prompt was cancelled). What makes this work, is passing the result as a ByRef argument, like this:
Public Function GetCasingSize(ByRef outResult As String) As Boolean
Do
Dim raw As Variant
raw = InputBox("Casing size?")
If VarType(raw) = vbBoolean Then
'handle cancelled prompt:
Exit Do
End If
If ValidateFractional(raw) Then
'handle valid input:
outResult = CStr(raw)
GetCasingSize = True
Exit Do
End If
'handle invalid input:
If MsgBox("The value '" & raw & "' is not valid. Try again?", vbYesNo) = vbNo Then
Exit Do
End If
Loop
End Function
Note the ValidateFractional function is its own concern - a separate, Private function would work, but I'd recommend making it Public, and unit-testing it to make sure it works as intended given a wide variety of edge-case inputs - and having it in a separate function means the logic in GetCasingSize doesn't need to change if the validation needs to be fine-tuned; for example this naive implementation uses the Like operator and would work for 5-1/4, but not for e.g. 15-5/8:
Public Function ValidateFractional(ByVal value As String) As Boolean
ValidateFractional = value Like "#[-]#/#"
End Function
Using Regular Expressions for this would probably be a good idea.