Karel the Robot Karel s World Plain made of streets avenues Corners or intersection Location determined by avenue street numbers Positive integers Origin Start is 1st avenue 1st street Copyright 2008 by Helene G Kershner Karel the Robot Walls Made of neutronium Obstacles Karel cannot pass through a wall Located Between streets Between avenues From origin Karel s World has a huge immoveable wall on his west side south side Copyright 2008 by Helene G Kershner Karel the Robot Beepers Pinging beeper Found at intersections Karel can do things with the beepers pick up one at a time carry put down Copyright 2008 by Helene G Kershner Karel the Robot Karel is a Robot Karel cannot think Karel is remarkable at his ability to follow instructions As long as these instructions are VERY detailed Copyright 2008 by Helene G Kershner Karel the Robot Karel s Capabilities Move forward move turn in place turnleft Knows which direction it is facing compass is equipped with three cameras forward right left These cameras have a block range Copyright 2008 by Helene G Kershner Karel the Robot Karel s Capabilities Karel can hear Can detect a beeper on the same corner Karel is standing Karel s has a Beeper Bag Stores beepers Soundproof Karel cannot hear beepers in the bag Karel can put beepers in the bag and remove beepers from the bag Copyright 2008 by Helene G Kershner Karel the Robot Karel s Abilities Not isn t very smart But Karel is very good at following instructions The algorithm or step by step set of instructions Karel follows is called a program Karel understands a very simple programming language By computer standards it is a high level language The computer inside Karel doesn t actually speak the language of our programs Our programs will have to be translated into the machine code 0 1 that the computer understands To do this we will compile our programs Copyright 2008 by Helene G Kershner Karel the Robot How does Karel know what to do Karel only does what we tell it to do We write a program that gives Karel its instructions Copyright 2008 by Helene G Kershner Karel the Robot Karel s Programming Language vocabulary punctuation marks rules of grammar Simple yet powerful Copyright 2008 by Helene G Kershner Karel the Robot 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 wall s Location number of beepers Karel s location direction Karel is facing Initial Situation Initialize Situation when Karel is assigned a task Final Situation After task is completed Copyright 2008 by Helene G Kershner Karel the Robot Primitive Instructions move turnleft pickbeeper putbeeper turnoff They allow Karel to move through world handle beepers Provide for avoiding obstacles transporting beepers Copyright 2008 by Helene G Kershner Karel the Robot Program Instruction Execution An instruction is Executed Run when Karel performs the task it is told to perform A program is Executed when the instructions in a program are carried out Copyright 2008 by Helene G Kershner Karel the Robot 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 When Karel turns off due to an error this is called an Error shutoff turnleft Karel pivots 90 degrees to left Location does not change Cannot cause error shutoff Why not Copyright 2008 by Helene G Kershner Karel the Robot Handling Beepers pickbeeper Karel picks up a beeper from the corner on which it is standing and deposits beeper in the beeper bag The pickbeeper command work on one beeper at a time There may be more than one beeper on a corner What if Karel tries to pick up a beeper when no beeper is at 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 Copyright 2008 by Helene G Kershner Karel the Robot Completing a Task When a task is complete Karel must be told to that the program is finished turnoff Karel must be shut down after task is completed Last instruction in every program Copyright 2008 by Helene G Kershner Karel the Robot What does a Karel the Robot Program look like BEGINNING OF PROGRAM BEGINNING OF EXECUTION Instructions ending with a semicolon END OF EXECUTION END OF PROGRAM The instructions are made up of the Primitive commands Karel understands Karel s Language has Reserved Words that structure the program BEGINNING OF PROGRAM BEGINNING OF EXECUTION instructions END OF EXECUTION END OF PROGRAM Copyright 2008 by Helene G Kershner Karel the Robot Errors Bugs Debugging Four kinds of errors can occur in Karel s Language Lexical Errors When Karel tries to read a word it doesn t understand Spelling Syntax Errors Errors in Grammer and Punctuation Ex Reserved words in the wrong order Missing semicolon Execution Errors When Karel is asked to do something it cannot do Pick up a bepper where none exists Walk into a wall Logic Errors Hardest to find and recognize Where program has no obvious errors but it doesn t solve the problem Or Karel executes part way and turns off Copyright 2008 by Helene G Kershner Karel the Robot Running Executing a Program Instructions between BEGINNING OF EXECUTION and END OFEXECUTION are acted on in order from top to bottom until a turnoff instruction or error shutoff is encountered How do we know what to ask Karel to do Simulate we model our solution on paper before we ever write a line in Karel s language We trace the program to make sure we have given Karel all the instructions needed Graph paper might be a good idea Verification What If we run Karel s program and our goal is not achieved We again trace the program seeing if we can find where be gave Karel incorrect information Verification Copyright 2008 by Helene G Kershner Karel the Robot Using Karel the Robot in Lab Different Windows World View Window Program View Window Execution Window Copyright 2008 by Helene G Kershner Karel the Robot Create a World Beeper inside a box Retrieve and Return Write a Program Copyright 2008 by Helene G Kershner Karel the Robot Problem statement Karel is to go to the open side of the box go inside and retrieve the beeper then go home Remember our Algorithm Planner Define the output Define the input Define the initial algorithm Refine the algorithm Define the program Copyright 2008 by Helene G Kershner Karel the Robot Define the