Visual Basic

Public Class Form1
     
        'The lines that have been drawn but not saved.
        Private lines As New List(Of Line)
     
        'The start point of the line currently being drawn.
        Private start As Point
     
        Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
            'Place a blank image in the PictureBox control.
            Me.PictureBox1.Image = New Bitmap(Me.PictureBox1.Width, Me.PictureBox1.Height)
        End Sub
     
        Private Sub PictureBox1_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
            'Remember the point at which the line started.
            Me.start = e.Location
        End Sub
     
        Private Sub PictureBox1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseUp
            'Remember the point at which the line ended.
            Dim [end] As Point = e.Location
     
            'Add the new line to the list.
            Me.lines.Add(New Line(Me.start, [end]))
     
            Dim area As New Rectangle(Math.Min(Me.start.X, [end].X), _
                                      Math.Min(Me.start.Y, [end].Y), _
                                      Math.Abs(Me.start.X - [end].X), _
                                      Math.Abs(Me.start.Y - [end].Y))
     
            'Inflate the rectangle by 1 pixel in each direction to ensure every changed pixel will be redrawn.
            area.Inflate(1, 1)
     
            'Force the control to repaint so the new line is drawn.
            Me.PictureBox1.Invalidate(area)
            Me.PictureBox1.Update()
        End Sub
     
        Private Sub PictureBox1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
            'Draw each line on the control.
            Me.DrawLines(e.Graphics)
        End Sub
     
        Private Sub Save()
            'Create a Graphics object from the Image in the PictureBox.
            Using g As Graphics = Graphics.FromImage(Me.PictureBox1.Image)
                'Draw each line on the image to make them permanent.
                Me.DrawLines(g)
            End Using
     
            'Clear the temporary lines that were just saved.
            Me.Clear()
        End Sub
     
        Private Sub Clear()
            'Clear all unsaved lines.
            Me.lines.Clear()
     
            'Force the control to repaint so the lines are removed.
            Me.PictureBox1.Refresh()
        End Sub
     
        Private Sub DrawLines(ByVal g As Graphics)
            For Each line As Line In Me.lines
                g.DrawLine(Pens.Black, line.Start, line.End)
            Next line
        End Sub
     
    End Class
     
    Public Class Line
     
        'The line's start point.
        Private _start As Point
     
        'The line's end point.
        Private _end As Point
     
        'The line's start point.
        Public Property Start() As Point
            Get
                Return Me._start
            End Get
            Set(ByVal value As Point)
                Me._start = value
            End Set
        End Property
     
        'The line's end point.
        Public Property [End]() As Point
            Get
                Return Me._end
            End Get
            Set(ByVal value As Point)
                Me._end = value
            End Set
        End Property
     
        Public Sub New()
            Me.New(Point.Empty, Point.Empty)
        End Sub
     
        Public Sub New(ByVal start As Point, ByVal [end] As Point)
            Me._start = start
            Me._end = [end]
        End Sub
     
    End Class

Dim x As Byte = 200
Dim y As Byte = 100
Dim z As Byte = (x + y) Mod 256

Dim x As Byte = 200
Dim y As Byte = 100
Dim z As Byte = (CInt(x) + CInt(y)) Mod 256