Sub Diagonal()
Dim Rng As Range, Fill, aFill
Dim isPlus, isMinus As Boolean
On Error Resume Next
Set Rng = Application.InputBox("Задайте диапазон", "Ввод данных", Type:=8)
If Rng Is Nothing Then Exit Sub
Fill = InputBox("Введите число (при вводе числа со знаком + или - будет введена прогрессия с шагом 1")
If Fill = "" Then Exit Sub
If InStr(Fill, "+") <> 0 Then
    isPlus = True
    Fill = Replace(Fill, "+", "")
    Else:
    If InStr(Fill, "-") <> 0 Then
    isMinus = True
    Fill = Replace(Fill, "", "")
    End If: End If
aFill = Val(Fill)
With Rng
    If .Columns.Count <> .Rows.Count Then
    If .Columns.Count > .Rows.Count Then Rng.Resize(.Rows.Count, .Rows.Count).Select Else _
    Rng.Resize(.Columns.Count, .Columns.Count).Activate
    End If
End With
With Rng
For I = 1 To .Columns.Count
    If isPlus Then .Cells(I, I) = aFill + 1 * (I - 1) _
    Else If isMinus Then .Cells(I, I) = aFill - 1 * (I - 1) Else .Cells(I, I) = aFill
Next I
.Cells(.Row, .Column).Select
End With
End Sub