Sub addCrossRefernce()
    Dim n As String
    On Error GoTo noReference
tryAgain:
    n = InputBox("enter number of equation to refer!")
    If n <> "" Then
        Selection.InsertCrossReference ReferenceType:="Equation", ReferenceKind:= _
            wdOnlyLabelAndNumber, ReferenceItem:=n, InsertAsHyperlink:=True, _
            IncludePosition:=False, SeparateNumbers:=False, SeparatorString:=" "
    End If
    Exit Sub
noReference:
    Err.Clear
    If MsgBox("There is no equation " & n & " in the document, do you want to enter another number?", _
        vbYesNo) = vbYes Then
        GoTo tryAgain
    End If
End Sub