[ديه زكرياء]

كود :

Public Class Form1

   Private Sub TextBox1_KeyUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyUp
       Dim p, c, m As Double
       If TextBox1.Text = "" Then
           p = 0
       Else
           p = Convert.ToDouble(TextBox1.Text)
       End If
       If TextBox2.Text = "" Then
           c = 0
       Else
           c = Convert.ToDouble(TextBox2.Text)
       End If
       m = p * c
       TextBox3.Text = m.ToString()
   End Sub

   Private Sub TextBox2_KeyUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox2.KeyUp
       Dim p, c, m As Double
       If TextBox1.Text = "" Then
           p = 0
       Else
           p = Convert.ToDouble(TextBox1.Text)
       End If
       If TextBox2.Text = "" Then
           c = 0
       Else
           c = Convert.ToDouble(TextBox2.Text)
       End If
       m = p * c
       TextBox3.Text = m.ToString()
   End Sub
End Class