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Lab 14: Conditionals

As usual, create a directory to hold today's files. All programs that you write today should be stored in this directory. 

$ cd ~/cs120/labs
$ mkdir lab14 
$ cd lab14

Practice Problem 1

Write the function minimum(number_1, number_2) that returns the minimum of the two parameters, number_1 and number_2. The function should not use the built-in min function. 








  
Practice Problem 2



  Write the function clamp(number, minimum, maximum) that
  returns the result of clamping the specified number into the range
  \([minimum, maximum]\).  That is, if number is below
  minimum, it returns minimum,
  if number is above
  maximum, it returns maximum, and otherwise
  it returns number.  The function should not use the
  built-in functions min and max.




  


  

  

    
  

  








Keyboard Control



  One of the benefits of conditional statements is the ability to
  change what code executes based on how the user reacts.  Using the
  graphics module, you can use the key_down() function to
  tell which key on the keyboard the user has pressed. Allowing the
  user the change how the program behaves is the first step to creating
  games within Python.



Details



  Download the graphics.py module, and store
  it in your directory for today's lab.  Create a new file
  called keyboard_control.py, which will create a graphics
  window.  Refer to the lecture today to
  setup a window for the graphics module.





  The rest of your program should allow the user to press
  the Left and Right arrow keys on the keyboard to
  move a drawn circle left and right on the string.




Example


  $ python3 keyboard_control.py





Hint



  
  

    
    
      
  • 
	You must first create and define a for loop which
	will control your animation.  Inside of this for loop is where
	you are going to draw your "red_circle.gif" image.
      
    • 
      
  • 
	Create variables to represent the circle's x and y
	coordinates.  The variables should be defined before the
	animation loop.
      
    • 

      
  • 
	The graphics module has multiple functions for getting
	keyboard input from the user.  The key_pressed
	function returns a boolean value depending on whether a key is
	currently being pressed.
      
    • 

      
  • 
	The key_pressed function has one parameter, a
	string, that represents a keyboard key.  The strings for left
	and right are "Left" and "Right" respectively.
      
    • 

      
  • 
	Add two conditional statements inside of your animation loop.
	One of them will check for the "Left" key, and one of them
	will check for the "Right" key.  If the left key is pressed,
	subtract some value from the circle's x location.  If the
	right key is pressed, add some value.
      
    • 
    

  






  
Challenge

  

    Add additional code to your program which will allow for the ball
    to move in any arbitrary direction.
  






Bouncing Ball



  With for loops and conditionals, we can now create complex looking
  behaviors.  One such program, which you have likely seen on every
  DVD player since the 1990's, is a logo which continually bounces
  around the string.  Today, using the graphics module and conditional
  statements, you will replicate a very simple form of this
  screen saver. 



Details



  Create a file called bouncing_ball.py.  In this file, you
  should draw a circle in the center of the graphics window.  You
  should animate the circle moving towards the right edge of the
  screen.  Once it reaches the right edge of the screen, the circle
  should "bounce" and move towards the left edge of the screen.  This
  should continue until the end of your animation loop.





Example


  $ python3 bouncing_ball.py





Hint



  
  

    
    
      
  • 
	You must first create and define a for loop which
	will control your animation.  Inside of this for loop is where
	you are going to draw your "red_circle.gif" image.
      
    • 

      
  • 
	Create variables to represent the circle's x and y
	coordinates.  The variables should be defined before the
	animation loop.
      
    • 
      
  • 
	In addition to position, you need to store a variable for the
	circle's speed.
      
    • 
      
  • 
	Every time you go through the for loop, you should use the
	accumulator pattern to modify the x location of the circle by
	the circle's speed.
      
    • 

      
  • 
	You can check if you have hit the edge of the graphics window
	by checking the position of the circle in the x direction
	against the two edges of your graphics window.
      
    • 

      
  • 
	If you hit the edge of the graphics window, you need to change
	the speed of the circle by multiplying the speed by \(-1\).
      
    • 
    

  






  
Challenge

  

    Right now, half of your circle will leave the window before it
    bounces.  Alter your code so that it does not leave the screen.