CS 110 Spring 2012 

Homework05: Mindbending with Recursion
plus Loops

Part I Due: Monday, February 27th at class time
Part II Due: Wednesday, February 29th at class time

 

Part 1 - Drawing with Recursion

Recursion 1 - Snowflake

Now we’ll use recursion to draw some neat patterns. We will again use the TurtleWorld module, just as we did for polygon.py and for the class exercise where we did our first Turtle-based recursion drawing.

Create a new program called Snowflake.py.  In the main function, create a TurtleWorld object and a Turtle object and move the turtle's position to (x,y) coordinate (-190, -50). The function below should help performing an absolute move.  Look carefully at the code below and try and understand exactly how it does its job. 

#-------------------------------------------------------------------------------
# moveto() moves the given turtle, t, to coordinates x, y without drawing a line
# and restoring the heading to its original orientation
#-------------------------------------------------------------------------------
def moveto(t, x, y):
   # Start by retrieving current coordinates and heading for turtle t
   currx = t.get_x()
   curry = t.get_y()
   currheading = t.get_heading()
   # Figure out how far to get to desired coordinates
   diffx = x - currx
   diffy = y - curry
   pu(t)
   lt(t,360-currheading)
   fd(t,diffx)
   lt(t,90)
   fd(t,diffy)
   lt(t,-90)
   lt(t,currheading)
   pd(t)

Now create a function called snow which returns nothing but has three parameters: a turtle object and two ints called iteration and length. 

The body of this function should do one of two things. 

First, if iteration is 0, all you should do is use the forward function on the turtle that was passed in, drawing forward the distance given by length.

The more complicated case is if iteration is greater than 0.  In that case, you will have 7 python steps.  Steps 1, 3, 5 and 7 all make (recursive) calls to the function snow.  Each call will be identical, and will be passed the turtle, iteration-1, and length/3.  That is, if we aren’t down to iteration 0 yet, our function will call the snow function four times with a lower iteration value and shorter lengths. 

Between each of these recursive calls, we’ll change the direction of our turtle.  To do this, you’ll use the lt() or rt() with an approriate angle.  The turns are 60 degrees to the left, 120 degrees to the right, and 60 degrees to the left, respectively.

Once you’ve got this, we can test it out.  Try calling the function snow in your main function with parameters (turtle, 0, 729).  (I picked 729 just because it is a power of 3, so when we do integer division by 3 repeatedly, we’ll still have the right integer).  Display the picture.  You should see a blue line (assuming the default turtle pen color) drawn across most of the image.  Try this again, but this time change the iteration count to 1.  This should add a kink to the middle of the line. 

Once you have this working, change your main function to make 6 calls to snow, where you start with snow(turtle, 0, 729) and go up to snow(turtle, 5, 729), incrementing iteration by 1 each time.  Between each call, reset the turtle position to its starting position, and change the pen color so you can distinguish the lines.

For example, a turtle named bob can change its color to red and reduce drawing time via the following commands:

bob.delay = 0.01
bob.set_pen_color('red')

Recursion 2 - Sierpinski’s carpet

Sierpinski’s carpet is defined as follows.  Start with an uncolored square.  Split it into 9 equal-sized squares.  Color in the middle square.  Draw Sierpinski’s carpet in the remaining 8 squares.  Here is what you should get:

 

 

Write a program called Carpet.py that creates this pattern.  Your function will probably need to take in a number of parameters: a reference to the window object, the current iteration (at zero, stop the recursion), the current width, and the current x and y coordinates of the top left of the area to be drawn. You will probably use the graphics library (from graphics import * or from myro import *) to implement this program.

Recursion 3 - Xander's Bubbles

Xander’s bubbles are defined as follows.  Start with an uncolored square.  Draw a circle in the middle of the square with radius one quarter the length of the square.  Then split the square into 4 equal pieces, and draw Xander’s bubbles in each quadrant.  You should get something like this:

 

 

Write a program called Bubbles.py that creates this pattern.  Again, your function will probably need to take in a number of parameters: the graphics window object, the current iteration, the current width, and the current x and y coordinates.

 

 

Part 2 - Practicing with Loops and Drawing

Loops 1 - Rock, Paper, Sissors

Write the game Rock, Paper, Scissors. In a file called RPS.py, write a program that does the following:

  1. Ask the user if they want the simple or the image based version of the game.
  2. For the simple version of the game, the playing screen consists of two control "buttons" (really just Rectangles with appropriate labels drawn in a GraphWin) with labels of 'Exit' and 'Again'. There are also three buttons for each of 'Rock', 'Paper', and 'Sissors'. The program should repeatedly:
  • Have the user select a choice of "Rock", "Paper", or "Sissors" by getting a mouse click and then to determine whether or not the click was in the "Rock" rectangle, the "Paper" rectangle, or the "Sissors" rectangle.
  • Once the user has made a selection, the program makes a random selection by generating a random integer from 1 to 3, inclusive, and use that random selection to determine the computer's rock, paper, or sissors.
  • Compare the computers selection with the user's selection and determine a winner of the round.
  • Display to the user (in some creative fashion) the Computer's selection, along with a message indicating who won.
  • Once the round is complete, the program should wait until one of the control buttons is clicked by the user, continuing on to another round if 'Again' is clicked, and exiting the program if 'Exit' is clicked.
  • When waiting for a control button click, clicks outside either of those two rectangles should have no effect.
  • When waiting for a rock/paper/sissors click, clicks outside either of those two rectangles should have no effect.
  • BE CREATIVE
  1. For the image based version of the game, you should find jpeg images on the web of a rock, a sheet of paper, and sissors, and use these images as the "buttons" for the user. The compter's selection should also show as an image.

Write and debug the code for the simple version of the game _first_, before spending the time on the image based version of the game. The majority of the grade for this will be based on correct and robust operation of the simple version of the game. ... I will try and make it "break" by clicking all over the place ... just like real users would do!

Loops 2 - Turingscraft

I have added the section from Chapter 7 in Turingscraft on numeric loops, also due for Wednesday, as the second assignment of Part II.

Uploading your lab

For HW05 Part I, folder hw05 should contain:

Snowflake.py

Carpet.py

Bubbles.py

For HW05 Part II, folder hw05 should contain:

RPS.py