[aftfm]

وهذا بطريقة ثانية

كود :

Dim SUM As Integer = 0
        For i As Integer = 0 To Me.DataGridView1.Rows.Count - 1
            SUM += Convert.ToInt32(me.DataGridView1(3,i).value)
        Next

        LBLSUM.Text = SUM.ToString()