22C:005 Problem Solving and Computing - Spring 2000

Homework 3 - Karel Programming Using Conditionals and Iteration

Due: Feb. 11  for Friday discussions, Feb. 14  for Monday discussions, and Feb. 16  for Wednesday discussions

Notes on Homework Assignments and What You Hand In

To turn in your Karel assignments, you are required to do the following two things:

• Send your TA a copy of your program text via email. You should be able to simply cut-and-paste your program text into your email message.  Your TA will provide you with his email address in discussion.
• Bring a printed, hard copy of your finished assignment to turn in at your discussion section.

In this assignment, your end goal will be to write a MazeWalker robot based off the Robot class (not the ur_Robot) that will be capable of escaping a maze.  You can always escape a maze if there are no islands by following the right or left wall.  In this assignment, you will eventually create a class of robot that will follow the wall to the right of the robot until it escapes the maze.

Part 1 - Questions

1. Q1: In which cases is a WHILE command useful and in which cases is a LOOP command useful?
2. Q2: Explain what the following code snippet does with the rectangular, beeper filled world given below (the robot is already placed in the world and it's name is Harold).  Note, Harold is not currently standing on a beeper.  Also, how many beepers will Harold pick up?


loop(15) {
   if (Harold.frontIsClear()) {
     if (Harold.nextToABeeper()) {
        Harold.pickBeeper();
     }
     else {
        Harold.move();
     }
   }
   else {
      Harold.turnLeft();
   }
}


 

3. Q3: Give an example of when it is beneficial to use the "!" operator in a conditional statement.
4. Q4: Note: Answer this question only when you have completed the programming portion of this assignment.


Explain the result of running your MazeWalker task on the following Karel World?

Part 2 - Code Snippets

1. Q1:  Write a snippet of code that will get the robot R2D2 from the initial configuration to the ending configuration.

Starting Configuration:     Ending Configuration:

I'll do this one for you.  To get the robot from the initial configuration to the ending
configuration, we would simply need the following commands:
 

R2D2.move();
 
Now, you can do the remaining snippets.
 
2. Q2: Write a snippet of code that will move the robot R2D2 from the initial configuration to the ending configuration.

Starting Configuration:      Ending Configuration:
 
3. Q3: Write a snippet of code that will move the robot R2D2 from the initial configuration to the ending configuration.

Starting Configuration:        Ending Configuration:
 
4. Q4: Write a snippet of code that will move the robot R2D2 from the initial configuration to the ending configuration.

 Starting Configuration:      Ending Configuration:
 
5. Q5: The snippets above represent the four (4) cases that the robot can be in if it needs to keep a wall to its right while moving around a room.  Notice that in each starting configuration the robot has a wall to its right and in each ending configuration, the robot has a wall to its right.   In computer science terms, this is called an "invariant".  In other words, the fact that the robot has a wall to its right should never vary.


Write a function called followWallRight, assuming that whenever a robot executes this function there is a wall directly to the right.  This function should maintain the invariant of having a wall directly to the right of the robot.  Use and combine the four configurations illustrated in Q1-Q4 to maintain the invariant.

For additional references, see Problem 17, pg. 141 and Problem 9, pg. 97 in the Karel++ book.

Part 3 - Programming the MazeWalking Robot

Initially, your robot will be placed in the middle of the maze, not next to a wall.  Your first task is to write a function that will get your robot situated so there is a wall to its right.

Next, use the function you wrote in Q5 above (followWallRight) to escape the maze.  You will know you have escaped the maze when you find the beeper which is placed just outside the maze.

Example Worlds

You will need to "download" the maze files onto your disk, or computer so you can use them later if you'd like. By downloading, we want you to save both WLD files to you disk so you can open them with the Karel program.   The files we provide are ONLY for IBM-Compatible PCs.  If you are using a Macintosh to program Karel, you will need to recreate the worlds by yourself.

• Maze 1 - Click Here to Download maze1.wld (HOLD THE SHIFT KEY DOWN WHEN YOU CLICK)
• Maze 2 - Click Here to Download maze2.wld (HOLD THE SHIFT KEY DOWN WHEN YOU CLICK)