CSC111 Lab 9 2011

--D. Thiebaut 13:15, 2 November 2011 (EDT)

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Working with Functions

• For this part, work in Idle or emacs and create the various functions this lab presents you, and test them in main().
• For example, if you are asked to write a function that receives a string as parameter and prints it with a box around it, you could write something like this:

def boxIt( string ):
    noChars = len( string )
    print( "-" * ( 2 + noChars  + 2 ) )
    print( "| " + string + " |" )
    print( "-" * ( 2 + noChars + 2 ) )

def main():
    boxIt( "hello!" )
    boxIt( "This is a very long string!" )
    boxIt( "" ) # empty string 

main()

• No need to add documentation for the code in this lab (or just in spots where you think you need to add markers for yourself)

Box

• Go ahead and create the boxIt() function above.
• Test it. Notice that I tested it with 3 different strings, one of them the empty string. It is important to test for "strange" conditions. An empty string is a totally valid string, and if our program is supposed to work with strings, it should work with empty strings as well without crashing.

Triple Boxes

• Add a new function called BoxIt3( s1, s2, s3), that receives 3 strings and prints each string in its own box.
• If you call your function in main() like this BoxIt3( "Hello", "There", "Smith College" ), it will print

---------
| Hello |
---------

---------
| There |
---------

-----------------
| Smith College |
-----------------

• Go ahead and test your new function. Test it with different strings.
• If your solution does not use the function BoxIt() created earlier, modify BoxIt3() so that it calls BoxIt() 3 times.

Multiple Boxes

• Add a new function called multipleBoxes( L ) that receives a list of strings and prints each string in the list with BoxIt().

• Here is are different possible ways one could test your function:

multipleBoxes( [ "Doc", "Grumpy",  "Happy", "Sleepy", "Bashful", "Sneezy", "Dopey" ] )

multipleBoxes( [ "Hello", "", "", "There!" ] )

multipleBoxes( "Hello Smith College!" . split() )

Functions Returning Values

Median of 3

• write a function that returns the median of 3 numbers.
• For example:

def median3( a, b, c ):
    # could it be b?
    if a <= b and b <= c:
          return b

    # if we're here, it's not b.  Could it be a?
    if b <= a and a <= c:
          return a

    # if we're here it's not b and not a.  It has to be c!
    return c


def main():
     print( median3( 10, 10, 20 ) )
     print( median3( 1, 2, 3 )
     print( median3( 6, 5, 7 )
     print( median3( 8, 10, 9 )

main()

• Modify the code above and make it simpler by remembering that you can put a, b, and c in a list, sort the list, and return the element at Index 1.

Second Smallest

• Write a function that receives a list of numbers (or strings), and that returns the second smallest of them.
• For example:

 L = [ 1, 10, 2, 3, 30, 40, 50 ]
 ss = secondSmallest( L ) 
 print( ss )                 # prints out 2

Testing Second Smallest

• Test the function you have just written, and print the contents of the List of numbers (or strings) before you call secondSmallest() and after you call it.
• You will likely see that your list has changed. (if not, then skip to the next problem)
• If it has changed it is because you are sorting the list inside your function, and the list is passed by reference to the function.
• Modify your function so that the list does not get modified by the function when it is passed.

Make User Name

• This one should make sense just by looking at what it returns.

  user = makeUserName( "Alex Smith" )
  print( user )
  # will print asmith
 
  print( makeUserName( "Mini Driver" ) )
  # will print mdriver

  print( makeUserName( "Alan J. Smith" ) )
  # will print asmith

• make sure the name returned is all lower-case.

Graphics with Functions

from graphics import *


def isInside( xc, yc, x1, y1, x2, y2 ):
    #
    # add your code here!
    #
    return 0

def main():
    w = 600
    h = 400
    x1 = 20
    y1 = 30
    x2 = w // 3
    y2 = h - y1
    win = GraphWin( "Click me to stop!", w, h )


    c = Circle( Point( w//2, h//4 ), 20 )
    c.setFill( "yellow" )
    c.draw( win )

    r = Rectangle( Point( x1, y1 ), Point( x2, y2 ) )
    r.setWidth(3)
    r.draw( win )

    dirX = 5
    dirY = 3
    
    while True:
        c.move( dirX, dirY )
        xc = c.getCenter().getX()
        yc = c.getCenter().getY()
        if not ( 0 <= xc <= w ): dirX = -dirX
        if not ( 0 <= yc <= h ): dirY = -dirY
        
        if isInside( xc, yc, x1, y1, x2, y2 )== 1:
            # center inside rectangle
            c.setFill( "red" )
        else:
            # center outside rectangle
            c.setFill( "yellow" )

        if win.checkMouse() != None:
            break

    win.close()

main()

• write the body of the function isInside( ) above. This function gets the coordinates of the center of the circle, and the coordinates of the points defining a rectangle, and it returns 1 when the center is inside the rectangle, and returns 0 when it is not.

Basically, the body of the function should be the python translation of this algorithm:

 if xc is between x1 and x2, and if yc is between y1 and y2,
       then return 1
  else return 0

• Once your function works, the circle should move freely around the graphics window, bouncing off the edges, and should change color as soon as its center enters the rectangle.