CSE 111
Karel the Robot'
Thanks to Dr. Kris Schindler for this
(and all Karel the Robot slides)
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
http://www.buffalo.edu/ubit/serviceguides/software/my-virtual-computinglab.html
Linked from course website
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
1st
avenue &
Locations
Relative
Absolute
1st
street
Streets
Origin
12
11
10
9
8
7
6
5
4
3
2
1
N
W
E
S
1 2 3 4 5 6 7 8 9 10 11 12
Avenues
Karel’s World
Walls
Made of neutronium
Obstacles
Karel cannot pass through a wall
Locations
Between streets
Between avenues
Form boundaries on west side & south side
Karel’s World
Beepers
Pinging beeper
Situated at intersections
Can be
picked up
carried
put down
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
Karel’s Capabilities
Karel can
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
Karel’s Capabilities
Karel can hear
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
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
Tasks & Situations
What is a task?
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
Primitive Instructions
Instructions
move
turnleft
pickbeeper
putbeeper
turnoff
They allow Karel to move through world &
handle beepers
Provide for avoiding obstacles & transporting
beepers
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
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?
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?
 Error shutoff
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?
 Error shutoff
Primitive Instruction Details
Completing a Task
turnoff
Karel must be shut down after task is completed
Last instruction in every program
Program Structure
General Structure
BEGINNING-OF-PROGRAM
BEGINNING-OF-EXECUTION
Instructions, all but last ending with a semicolon
(;)
END-OF-EXECUTION
END-OF-PROGRAM
Executing a Program
Instructions between BEGINNING-OFEXECUTION 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
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
Saving Your Work
Programs and worlds can be saved!
Sample Program
Task
Pick up beeper located at intersection of avenue 3,
and street 4
Karel is at the intersection
of avenue 1 and street 1
facing north
Beeper placed at
intersection of avenue
3 and street 4
Streets
Initial World
12
11
10
9
8
7
6
5
4
3
2
1
N
W
E
S
Beeper
1
Karel initially
has zero beepers
in beeper bag
Karel’s Initial
Position
(facing north)
1 2 3 4 5 6 7 8 9 10 11 12
Avenues
Sample Program
Program
BEGINNING-OF-PROGRAM
BEGINNING-OF-EXECUTION
turnleft;
turnleft;
turnleft;
move;
move;
turnleft;
move;
move;
move;
pickbeeper;
turnoff
END-OF-EXECUTION
END-OF-PROGRAM
Sample Program
Streets
Final World
12
11
10
9
8
7
6
5
4
3
2
1
N
W
E
S
Karel’s Final
Position
Karel ends up
with one beeper
in the beeper bag
1 2 3 4 5 6 7 8 9 10 11 12
Avenues
References
Richard E. Pattis (revised by Jim Roberts &
mark Stehlik), Karel the Robot, John Wiley &
Sons, Inc., 2nd edition, 1995, pp 1-11
Your Task in Lab
Run tutorial, learning how to program using
Karel the Robot