Mettre le signe négatif dans certaines cellules

Option Explicit

Sub C_Negatif()
    ' liste des feuilles à traiter, mettre une , finale
    Const listeF As String = "DETTES,47511 DETTES,475 MUT,"

    Dim sh As Worksheet, c As Range
    Dim derlig As Long, lig As Long, colM As Long
    
    Application.ScreenUpdating = False
    For Each sh In Worksheets
        If InStr(listeF, sh.Name & ",") > 0 Then
            derlig = sh.Cells(Rows.Count, "D").End(xlUp).Row
            'recherche colonne Montant, colonne Sens supposée juste après
            ' attention, sensible aux majuscules/minuscules
            Set c = sh.Rows(1).Find("montant", LookIn:=xlValues)
            If c Is Nothing Then
                MsgBox "'montant' non trouvé dans la feuille " & sh.Name
            Else
                colM = c.Column ' colonne "montant"
                For lig = 2 To derlig
                    If sh.Cells(lig, colM) > 0 And sh.Cells(lig, colM + 1) = "C" Then
                        ' si montant positif et sens C
                        sh.Cells(lig, colM) = -sh.Cells(lig, colM)
                    End If
                Next lig
            End If
        End If
    Next sh
    Application.ScreenUpdating = True
End Sub