#-----
# contract : circle_area : number -> number
# purpose: determine the area of a circular disk
#          whose radius is <radius>
# example: abs (circle_area(5) - 78.53975 ) < .001
#-----

PI = 3.14159

from math import *

def circle_area(radius):
    return PI * pow(radius, 2)

#-----
# contract : ring_area : number number -> number
# purpose: determine the area of a ring whose outer
#          radius is <outer> and whose "hole"
#          has radius <inner>
# example: abs (ring_area(10, 5) - 235.61925 ) < .001
#-----

def ring_area(outer, inner):
    outer_area = circle_area(outer)
    hole_area = circle_area(inner)

    return outer_area - hole_area

#-----    
# contract: name_in_lights: anything -> void
# purpose: print <thing> between two lines of 20 asterisks
# example: name_in_lights(13) would cause the following
#          to be printed to the screen (ignoring the comment marks!):
# ********************
# 13
# ********************

def name_in_lights(thing):
    print "********************"
    print thing
    print "********************"

name_in_lights(13)

#-----
# contract: greet_rain: void -> void
# purpose: greet the rain, printig to the screen
# example: if you call greet_rain(), the following
#          should be printed to the screen:
# hello, rain!

def greet_rain():
        print "hello, rain!"

#-----
# contract: show_name : void -> void
# purpose: asks the user for his/her name, and then prints it
#          between two rows of 20 asterisks
# example: if I call show_name(), I will see a prompt:
#
# type your name:
#
# ...if I then type George, the following will be printed
# to the screen:
#
# ********************
# George
# ********************

def show_name():
    name = raw_input("type your name:")

    name_in_lights(name)