[aljzazy]

كود :

Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs)
   Dim d1 As DateTime
   Dim d2 As DateTime

   For i As Integer = 0 To dataGridView1.RowCount - 1
       d1 = Convert.ToDateTime(dataGridView1.Rows(i).Cells(2).Value)
       d2 = Convert.ToDateTime(dataGridView1.Rows(i).Cells(1).Value)
       Dim ts As TimeSpan = d1 - d2
       dataGridView1.Rows(i).Cells(3).Value = ts.Days
   Next
End Sub