How to transfer a value from one cell to another

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VB

i have a datagridview and i want to transfer a decimal value from one column cell to another. the second cell is also decimal type.
when i try to run i receive a message saying that "is not a valid value for decimal" or "commit error". Please help me.

What I have tried:

here is my code.

        Dim p As Integer = 0
        Do While p <= DataGridView1.RowCount - 1
            For q As Integer = 3 To 2 Step -1
                If DataGridView1.Rows(p).Cells(1).Value <> "rep" Then


                    If DataGridView1.Rows(p).Cells(q).Value IsNot Nothing Then
                        'DataGridView1.Rows(p).Cells(q).GetType.Name

                        Dim column_type = (DataGridView1.Rows(p).Cells(q)).ValueType
                       Dim column_type2 = (DataGridView1.Rows(p).Cells(q + 2)).ValueType

                        If column_type Is GetType(String) Then
                            MsgBox("ok")

                        Else
                            MsgBox(column_type.ToString & "mmmm")
                            MsgBox(column_type2.ToString & "nnn")
                            MsgBox(DataGridView1.Rows(p).Cells(q).Value)
                            MsgBox(DataGridView1.Rows(p).Cells(q + 2).Value & "hhh")
                        End If

        DataGridView1.Rows(p).Cells(q + 2).Value = DataGridView1.Rows(p).Cells(q).Value
                        DataGridView1.Rows(p).Cells(q).Value = ""
                    End If
                End If

            Next
            p = p + 1
        Loop