Run update21, if you haven't already, to create cs21/labs/04. Then cd into your cs21/labs/04 directory and create the python programs for lab 4 in this directory (we are not giving you starter files this time). And remember, handin21 looks for your lab 4 assignments in that cs21/labs/04 directory!

$ update21
$ cd cs21/labs/04
$ vim grid.py

Your programs are graded on both correctness and style. Please review the comments regarding programming style on the main page.

Write a program called grid.py that asks the user to specify a line spacing, and then draws (using the Zelle graphics library ) a grid of horizontal and vertical lines with that spacing in a graphics window with dimensions 500x500.

Below are some screenshots from such a program.

$ python grid.py

   This program draws a grid of lines on the graphics
   window. Please enter the spacing you want below.
        
grid spacing: 100

$ python grid.py

   This program draws a grid of lines on the graphics
   window. Please enter the spacing you want below.
        
grid spacing: 25

$ python grid.py

   This program draws a grid of lines on the graphics
   window. Please enter the spacing you want below.
        
grid spacing: 78

Winter is coming! :) Use the Zelle graphics library to draw a snowman.

Open a file called snowman.py and create a program that draws a snowman using the graphics library. Here are some guidelines to follow:

• Your program should display the snowman in the graphics window until the user clicks the mouse.
• Your program should tell the user (in the graphics window) that they need to click to end the program. After the mouse click your program should close the graphics window and end.
• Use at least 4 different colors in your picture, and include at least eyes, nose, and two other features (background scene, hat, pipe, scarf, buttons, etc).
• For symmetrical features (such as eyes), remember to use the clone method to make a copy of the original shape. Then draw the cloned shape in the window and move it to the desired location.
• You may want to use the setCoords method of the GraphWin object to adjust the coordinates of the window. You can read about this method on page 152 of the textbook.

Be creative (not all features can be circles!). One example is shown below.

Write a program called soccer.py that draws a soccer field, based on mouse clicks from the user. Have the user click once for the left side of the field and once for the right side. Then draw a soccer field to scale. Also have the user click a few times to place some player positions (x's and o's) on the field (see images below).

Hints and tips:

• you only need to draw the field edges, center circle, midfield line, two goals, and a few player positions
• make sure you tell the user what each click is for (left edge, right edge, close window, etc)
• a soccer field is 130 yards long and 100 yards wide. If the user determines how long the field is with two mouse clicks (say, fx), then the width of the field will be fy = fx*(100.0/130.0)
• always center the field vertically in a graphics window of width x height = 600x500
• the center circle has a radius of 10 yards. Again, given a field length fx, the scaled radius of the center circle will be r = fx*(10.0/130.0)
• the goals are 8 yards long, so scaled that is gw = fx*(8.0/130.0) (see images below). Assume they are 4 yards deep, that is gd = gw/2.0
• here is a field diagram showing each dimension you need to calculate after determining fx from the user mouse clicks:

Here are some screenshots from our soccer.py program.

Note: Extra Challenge Problems are not a part of the graded lab assignment, and are not required. Please do not attempt these problems until you have completed the required parts of this lab. Feel free to hand them in, but again, they are not graded.

For the grid program, write another program (subgrid.py) that divides each grid box into a 4x4 subgrid, using thinner lines and color. Also, allow for different x and y grid spacings.

For the soccer program, include all field markings.

Once you are satisfied with your programs, hand them in by typing handin21 at the unix prompt. You may run handin21 as many times as you like, and only the most recent submission will be recorded.