1. Thanks to Dr. Kris Schindler for this (and all Karel the Robot slides)
CSE 111
Karel the Robot'
Thanks to Dr. Kris Schindler for this (and all Karel the Robot slides)

2. Logging into Karel Available on all cybrary computers
From home, or in lab use UB Virtual Computing Lab
We will go over this in lab
Guide available at guides/software/my-virtual-computing- lab.html
Linked from course website

3. Karel’s World Plain made of streets & avenues Corners
Describe intersection of streets and avenues
Referenced by
avenue number
street number
Avenue & street numbers
Positive integers
Origin
1st avenue & 1st street
Locations
Relative
Absolute

4. Karel’s World Walls Made of neutronium Obstacles Locations
Karel cannot pass through a wall
Locations
Between streets
Between avenues
Form boundaries on west side & south side

5. Karel’s World Beepers Pinging beeper Situated at intersections Can be
picked up
carried
put down

6. Karel’s Capabilities Can Karel the Robot think?
Take a look at the path following example
Karel navigates a maze
The configuration of the maze is unknown to Karel
The end of the maze is determined by a single beeper placed at the exit

7. Karel’s Capabilities Karel can Karel knows Karel is equipped with
move forward
turn in place
Karel knows
which direction it is facing
Karel is equipped with
three cameras
Cameras face
forward
right
left
Range
1/2 block

8. Karel’s Capabilities Karel can hear Karel’s Beeper Bag
Can detect a beeper on the same corner Karel is standing
Karel’s Beeper Bag
Stores beepers
Karel can put beepers in the bag and remove beepers from the bag
Soundproof
Karel cannot hear beepers in the bag

9. Karel’s Tasks How does Karel know what to do?
Karel can follow a detailed set of instructions
Called a program
The language Karel understands is called a programming language
Defined by
vocabulary
punctuation marks
rules of grammar
Simple, yet powerful

10. Tasks & Situations What is a task? What is a situation?
Something we want Karel to do
What is a situation?
Description of Karel’s world
Includes
Size & location of each wall
Location & number of beepers
Karel’s location & direction Karel is facing
Initial Situation
Karel’s world at beginning of task
Includes Karel’s initial location, direction Karel is facing, and the number of beepers in the beeper bag
Final Situation
Karel’s world after task is completed
Includes Karel’s final location, direction Karel is facing, and the number of beepers in the beeper bag

11. Primitive Instructions
move
turnleft
pickbeeper
putbeeper
turnoff
They allow Karel to move through world & handle beepers
Provide for avoiding obstacles & transporting beepers

12. Program & Instruction Execution
An instruction is executed when Karel performs the action associated with the instruction
A program is executed when the instructions in a program are carried out

13. Primitive Instruction Details
Changing Position
move
Karel moves forward one block
Karel remains facing in the same direction
If a wall is in Karel’s way & a move instruction is executed, Karel shuts off
Error shutoff
turnleft
Karel pivots 90 degrees to left
Location does not change
Cannot cause error shutoff
Why not?
There is no turnright instruction
How does Karel turn right?

14. Primitive Instruction Details
Handling Beepers
pickbeeper
Karel picks up a beeper from the corner on which it is standing and deposits the beeper in the beeper bag
Only one beeper is picked up
Note that there may be multiple beepers on a corner
What if no beeper exists on the corner?
Error shutoff
putbeeper
Karel takes a beeper out of beeper bag and places beeper on corner
What if there are not any beepers in the bag?

15. Primitive Instruction Details
Handling Beepers
pickbeeper
Karel picks up a beeper from the corner on which it is standing and deposits the beeper in the beeper bag
Only one beeper is picked up
Note that there may be multiple beepers on a corner
What if no beeper exists on the corner?
Error shutoff
putbeeper
Karel takes a beeper out of beeper bag and places beeper on corner
What if there are not any beepers in the bag?

16. Primitive Instruction Details
Completing a Task
turnoff
Karel must be shut down after task is completed
Last instruction in every program

17. Program Structure General Structure BEGINNING-OF-PROGRAM
BEGINNING-OF-EXECUTION
Instructions, all but last ending with a semicolon (;)
END-OF-EXECUTION
END-OF-PROGRAM

18. Executing a Program
Instructions between BEGINNING-OF- EXECUTION and END-OF-EXECUTION sequentially executed until a turnoff instruction or error shutoff is encountered.
Since Karel is a cyber robot, we simulate & trace the program
Simulate
Systematically execute program just as Karel would perform each instruction
Trace
Step through program, maintaining each step
Verification
Simulation & tracing through program to ensure that it works properly

19. Using Karel the Robot in Lab
Enter program
Compile program
Checks for syntax errors, getting program ready to run
Setup initial world
Initialize world
Execute program
Run
Execution begins
Ends with either:
a proper shutdown (turnoff instruction)
a runtime error
Trace
Step
Unstep

20. Saving Your Work
Programs and worlds can be saved!

21. Sample Program Task Initial World
Pick up beeper located at intersection of avenue 3, and street 4
Initial World
Karel is at the intersection of avenue 1 and street facing north
Beeper placed at intersection of avenue and street 4

22. Sample Program Program BEGINNING-OF-PROGRAM BEGINNING-OF-EXECUTION
turnleft;
move;
pickbeeper;
turnoff
END-OF-EXECUTION
END-OF-PROGRAM

23. Sample Program
Final World

24. References
Richard E. Pattis (revised by Jim Roberts & mark Stehlik), Karel the Robot, John Wiley & Sons, Inc., 2nd edition, 1995, pp 1-11

25. Your Task in Lab
Run tutorial, learning how to program using Karel the Robot