فور نكست

Public Class Math

    Function Add(ByVal No1 As Double, ByVal No2 As Double) As Double
        Add = No1 + No2
    End Function

    Function Subtract(ByVal No1 As Double, ByVal No2 As Double) As Double
        Subtract = No1 - No2
    End Function

    Function Multiple(ByVal No1 As Double, ByVal No2 As Double) As Double
        Multiple = No1 * No2
    End Function

    Function Divide(ByVal No1 As Double, ByVal No2 As Double) As Double
        Divide = No1 / No2
    End Function

    ' you can write here the same functions that handles any kinds
    'of math operations, like above.

End Class

then instantiate a new object from Class "Math"

Private MathObj As New Math()

  

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If TextBox1.Text = Nothing And TextBox2.Text = Nothing Then
            MessageBox.Show("You must enter a No. in both fields", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit Sub
        End If

        If TextBox1.Text = Nothing Then
            MessageBox.Show("You must enter a No. in the first field", "1st Field", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit Sub
        End If
        If TextBox2.Text = Nothing Then
            MessageBox.Show("You must enter a No. in the second field", "2nd Field", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit Sub
        End If

        Label1.Text = MathObj.Add(TextBox1.Text, TextBox2.Text)

    End Sub

    
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        If TextBox3.Text = Nothing Then
            MessageBox.Show("You must enter a No. in the first field", "2nd Field", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit Sub
        End If
        If TextBox4.Text = Nothing Then
            MessageBox.Show("You must enter a No. in the second field", "2nd Field", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Exit Sub
        End If
        Label3.Text = MathObj.Subtract(TextBox3.Text, TextBox4.Text)

    End Sub

...hope that will help