Microsoft Small Basic

Program Listing:

' Sierpinski Triangle created using the Chaos Game algorithm (http://en.wikipedia.org/wiki/Sierpinski_triangle)
' By Neil Kendall, August 2011
' SmallBASIC Challenge of the Week 9 - Advanced Challenge (http://social.msdn.microsoft.com/Forums/en-US/smallbasic/thread/15a4a5bf-98d8-42f9-93ce-7246ef584a2c)
' Triangle vertices created at random, initial start point is also random [possible extension - see below].

Size=400 ' Max sixe of Graphics Window - change this to suit your screen resolution
Iterations=30000 ' Change this value for number of pixels plotted. The higher the value the better the picture, but slower to draw.

TriangleNumber=1 ' Keep track of number of triangles plotted

' Set up graphics window
GraphicsWindow.Height=Size
GraphicsWindow.Width=Size
GraphicsWindow.BackgroundColor="Blue"
GraphicsWindow.BrushColor="White"

Loop: ' Start again after each triangle is plotted

GraphicsWindow.Clear()
TriangleColour=graphicswindow.GetRandomColor() ' Get a random colour to draw the triangle
GraphicsWindow.DrawText(5,5,"Random Sierpinski Triangle. Number "+TriangleNumber) ' Display triangle number

' Generate 3 random vertices for the triangle
' Possible extension for you - make sure the random vertices 'look' like a triangle - E.g. Some sets of 3 random vertices are almost in a straight line so the triangle does not look good.
Vertex1X=Math.GetRandomNumber(Size)
Vertex1Y=Math.GetRandomNumber(Size)
Vertex2X=Math.GetRandomNumber(Size)
Vertex2Y=Math.GetRandomNumber(Size)
Vertex3X=Math.GetRandomNumber(Size)
Vertex3Y=Math.GetRandomNumber(Size)

' Set Initial Plot Position (random). If this position is within the area of the random triangle then random pixels outside of the triangle will not be plotted. [Very good extension exercise for you!]
CurrentPosX=Math.GetRandomNumber(Size)
CurrentPosY=Math.GetRandomNumber(Size)

For count=0 To Iterations
  RandomVertex=math.GetRandomNumber(3)  ' Choose a random vertex

  If RandomVertex=1 Then
    NewPositionX=(CurrentPosX+Vertex1X)/2 ' Calculate the X-coord of the midpoint between the current position and Vertex1
    NewPositionY=(CurrentPosY+Vertex1Y)/2 ' Calculate the Y-coord of the midpoint between the current position and Vertex1
    GraphicsWindow.SetPixel(NewPositionX,NewPositionY,TriangleColour)
    CurrentPosX=NewPositionX ' Make the current position the new calculated position
    CurrentPosY=NewPositionY
  EndIf

  If RandomVertex=2 Then
    NewPositionX=(CurrentPosX+Vertex2X)/2 ' Calculate the X-coord of the midpoint between the current position and Vertex2
    NewPositionY=(CurrentPosY+Vertex2Y)/2 ' Calculate the Y-coord of the midpoint between the current position and Vertex2
    GraphicsWindow.SetPixel(NewPositionX,NewPositionY,TriangleColour)
    CurrentPosX=NewPositionX ' Make the current position the new calculated position
    CurrentPosY=NewPositionY
  EndIf

  If RandomVertex=3 Then
    NewPositionX=(CurrentPosX+Vertex3X)/2 ' Calculate the X-coord of the midpoint between the current position and Vertex3
    NewPositionY=(CurrentPosY+Vertex3Y)/2 ' Calculate the Y-coord of the midpoint between the current position and Vertex3
    GraphicsWindow.SetPixel(NewPositionX,NewPositionY,TriangleColour)
    CurrentPosX=NewPositionX ' Make the current position the new calculated position
    CurrentPosY=NewPositionY
  EndIf

EndFor

TriangleNumber=TriangleNumber+1

Goto Loop