Public Class Funktionsplotter

    Dim berechnet As Boolean = False


    Private Function F(ByVal x As Single) As Single
        F = x * x
    End Function

    Private Function G(ByVal x As Single) As Single
        If (x < 10) Then
            G = 5 * x
        Else
            G = 20 * x - 150
        End If


    End Function
    Private Sub ButtonEnde_Click(sender As System.Object, e As System.EventArgs) Handles ButtonEnde.Click
        Me.Close()
    End Sub

    Private Sub ButtonBerechnen_Click(sender As System.Object, e As System.EventArgs) Handles ButtonBerechnen.Click
        REM Berechnen
        Dim x, y As Single

        For x = 0 To 20 Step 0.1
            y = F(x) - G(x)


            ListBox1.Items.Add(Format(x, "00.0") + vbTab + Format(y, "000.00"))

        Next

        berechnet = True
        Me.Invalidate()

    End Sub

    Private Sub Form1_Paint(sender As Object, e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint

        Dim x, y As Single
        Dim xpos, ypos As Integer
        If (berechnet) Then

            Dim whiteBrush As New Drawing.SolidBrush(Color.White)
            Dim blackPen As New Drawing.Pen(Color.Black, 1)
            Dim fontObj As Font
            fontObj = New System.Drawing.Font("Times", 10, FontStyle.Bold)



            e.Graphics.FillRectangle(whiteBrush, 180, 30, 320, 280)
            e.Graphics.DrawLine(blackPen, 180, 170, 500, 170)
            e.Graphics.DrawLine(blackPen, 180, 30, 180, 310)
            e.Graphics.DrawString("Plot", fontObj, Brushes.Black, 190, 40)

            REM Urspung bei 180,170 x-Ausdehnung: +320, y-Ausdehnung: -140, +140

            For x = 0 To 20 Step 0.1
                y = F(x) - G(x)

                xpos = 180 + x / 20 * 320
                ypos = 170 - (y / 150) * 140
                e.Graphics.DrawLine(blackPen, xpos, 170, xpos, ypos)

            Next
        End If

    End Sub


    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub
End Class