Option Explicit
Sub auto_open()

Dim myRng As Range
Dim myCell As Range

Set myRng = Worksheets("sheet1").Range("a1:A1000")

For Each myCell In myRng.Cells
With myCell
.Offset(0, 2).Validation.Delete
If IsNumeric(.Value) _
And .Text Like "#.#" Then
With .Offset(0, 2)
.Value = ""
With .Validation
.Add Type:=xlValidateList, _
AlertStyle:=xlValidAlertStop, _
Operator:=xlBetween, Formula1:="Yes,No"
.IgnoreBlank = True
.InCellDropdown = True
.InputTitle = ""
.ErrorTitle = ""
.InputMessage = ""
.ErrorMessage = ""
.ShowInput = True
.ShowError = True
End With
End With
End If
End With
Next myCell
End Sub

the above code checks if the format of the Column A is of the format
integer.integer (2.2)
how do i check the format integer.integer.integer.integer (2.2.2.2)
i tried #.#.#.# it did not work