The viewer works in Chrome, Edge, Firefox, and Safari. The web address for the workshop is

Transcription

1 LOGIC WITH KAREL INTRODUCTION TO CODING AND LOGICAL REASONING Karel is a robot who runs around a 12 x 15 maze, collecting and placing objects. That may sound simple, but Karel teaches all kinds of sophisticated logical structures. The 24 problems in this workshop start with basic movements, then dive into scripted commands, repeat loops, conditions, functions, and so much more. As you through the exercises, think about how these logical structures could be used to solve real world problems. Don t be surprised if you start to see the world as repeated patterns, recursive calls, and logical operators! GETTING STARTED You will need a device connected to the Internet to do these problems. Most devices will work, including PC s, Macs, Chromebooks, and tablets. Your phone will not, as the screen is too small to accommodate the Karel viewer. The viewer works in Chrome, Edge, Firefox, and Safari. The web address for the workshop is You will see the 24 levels laid out as tiles. Click on a tile and the viewer will open. You may see a screen or two before the working screen, explaining a concept or adding to the storyline. The viewer has two sections. Type your code on the side, and view the results on the. BASIC INSTRUCTIONS Karel syntax is simple. However, there are a few rules. o Words are lower case and must be spelled correctly. Keywords will change color when typed correctly. o All commands are written on separate lines. o Indent two spaces for the body of a loop. Press the ld arrow to run the program. To speed up Karel s movement, to Settings and change the speed to Fast. You can step through the code line by line by pressing the black arrow. Press the black circle with the rotating arrow to reset the maze. Press the red and white tar to use the code template. This will show the code structure. Don t worry about making mistakes. The program will suggest errors and fixes, and nothing will explode. Have fun! If you stuck, the answers are included in this handout.

2 THE 24 PROBLEMS 1 - MANUAL MODE Before we start scripting, practice navigating the maze in Manual Mode, either by pressing the icons, or by using the arrow keys for movement, SHIFT for, and CTRL for Karel moves one square forward. Karel turns 90 to his. Karel turns 90 to his. Karel picks up an object. Karel places an object. 2 SIMPLE COMMANDS Practice the same basic commands by typing them, one command per line. 3 REPEAT LOOP I Any set of commands which needs to be repeated can be written as a loop, starting with the number of times the commands are to be repeated. The body of the loop is indented 2 spaces.

3 4 REPEAT LOOP II In this problem, repeat loops are embedded in a longer program. There are several solutions. This one has only 15 lines of code and includes a nested loop (see Problem 5). repeat 10 repeat 2 5 NESTED LOOPS Nested loops are used for patterns within patterns. Notice how indentation shows the relationships. repeat 4 6 CONDITIONS Conditions create flexibility in a program. Karel is no longer restricted to fixed patterns, but can respond to his environment. Karel has a large library of defined objects: in this case, a spider. repeat 10 if spider

4 7 - KEYWORD ELSE Karel now has choices to make: if the condition is present (if), he does one set of actions. If it is not present (), he does another. repeat 11 if mark 8 KEYWORD OR Karel can decide based on the presence of one or another object. The keywords are connected by the Boolean operator or. repeat 18 if coin or nug if wall if snake 9 WHILE LOOP Karel will continue to repeat a set of actions as long as the while condition is met. while acid

5 10 FIRST MAZE ALGORITHM An alrithm is a process used to solve a problem, using certain rules. We want the alrithm to work consistently and make best use of resources. We may want it to be flexible enough to solve different conditions. if wall if wall if key 11 CUSTOM COMMANDS I If we want to use a set of actions several times in a program, we can define a command using def, then call it in the main program. Comment lines begin with a # symbol, which tells the program to ignore that line. Comments are used to explain what is ing on in the program. # Command 'waterbox' from level 11.5: def waterbox repeat 4 repeat 2 waterbox waterbox waterbox 12 SECOND MAZE ALGORITHM This program includes a classic alrithm that can be used to follow along barriers of any shape. # Move along the wall and collect # a banana if there is one: def move if banana while wall move

6 13 CUSTOM COMMANDS II More practice with custom commands. This program is systematic, using the same set of alrithms for each row. # Custom command from previous level: def floor repeat 14 if apple or orange while wall floor while not wall 14 VARIABLES I Karel can collect information as he es. In this case a variable missing starts with a value of 0, and is increased every time Karel finds a gap in the fence. At the end, Karel reports the total number of missing fence sections using the print command. missing = 0 if not wall inc(missing) print("missing pieces:", missing) 15 VARIABLES II More practice with variables. Karel practices a positioning alrithm which places him to the of the row before counting each crate. def row # Locate -most crate: while crate # Count crates: r = 0 while crate inc(r) return r result = row print("there are", result, "crates!")

7 16 GPS We can identify the exact location of Karel on our grid, by numbering each horizontal square from to starting from 0 (gpsx), and each vertical square from bottom to top (gpsy). Note the operator!= stands for not equal to. if gpsy!= 2 17 BOOLEANS True and False are used to make logical deductions, and are at the heart of comer programming. In this case, Karel assumes there is a bottle in every corner until he finds one that is not. It only takes one missing bottle to switch from True to False. # Return True if there was a bottle in # every corner, otherwise return False: def corners b = True repeat 4 while not wall b = (b and bottle) if bottle return b success = corners if success print("there was a bottle in each corner!") print("one or more bottles were missing!") 18 MAXIMUM Karel can test for a maximum (or a minimum) by using an alrithm that compares each new value to the previous one. If it is less, then the previous value is retained. If it is more, then the previous value is replaced. # Collect one column and return its height: def column h = 0 while bulb inc(h) while not wall return h # Collect all columns and return the maximum height: def maximum m = 0 print("maximum started at", m) repeat 9 c = column if m < c Continued next page

8 m = c print("maximum updated to", m) return m height = maximum print("height is", height) 19 LISTS I Karel can generate Python lists to store and return data. Here, Karel is recording the location of orchids in a jungle. L = [] while not wall if orchid print("orchid found at", [gpsx, gpsy]) L.append([gpsx, gpsy]) while not wall print("orchids found at positions", L) 20 LISTS II In this case, Karel is using a list to map out a path and store each movement and turn in a list. P = [] counter = 0 while (not wall) and (not home) inc(counter) P.append(counter) if wall P.append(False) P.append(True) # Print the list: print("p =", P)

9 21 RANDOMNESS Karel can use random numbers to make choices. In this case, Karel randomly es forward, then or until he finds a rug. Karel only needs to collect one to end the program. # THERE ARE MANY SOLUTIONS. ALL OF THEM SHOULD BE OK AS LONG # AS THEY SOMEHOW COMBINE RANDOMLY GOING FORWARD AND TURNING. while empty if rand if not wall if rand if rug 22 RECURSION I Karel uses recursion to call a command until a stopping condition is achieved, in this case: home. Karel will continue to collect shields and place them in boxes until he is stopped by the home square. Rather than use a while loop, this command calls itself. # Custom command walk: def walk # Stopping condition: if not home if shield if box # Recursive call: walk return walk 23 RECURSION II Karel uses recursion within a more complex function that counts objects and returns a statement which varies according to what he finds. # Recursive function: def bounty # Stopping condition: if not home if candy or lollipop return bounty + 1 return bounty return 0

10 print("i collected", bounty, "candies.") 24 FINAL CHALLENGE How will we solve this challenge? Will it be with repeat loops, conditions, lists, random numbers, recursions, counting variables? In this case the patterns are clearly well defined and repeatable. repeat 4 repeat 2 FINAL THOUGHTS Karel was designed to teach logical reasoning. Karel was designed as a teaching language by Richard Pettit at Stanford University in 1983, based on Pascal. This version is based on Python, a language commonly used today in science, math, and design. Python has extensive open source libraries of commands, some powerful features, and the syntax is simple compared to other advanced languages. Students can learn and practice many logical structures using Karel, with or without the maze. These 24 problems are just a few examples. It isn t difficult to see how programming can be used to solve problems, collect and store data, navigate, and even generate new ideas in the real world. NCLab offers a complete Karel course, which can be followed by other Python-based courses. Please visit nclab.com for more information on courses, trainings, or to apply for a free individual trial to explore these courses. Free trials are available to teachers, librarians, and administrators. We hope you have enjoyed your exploration of logic with Karel the Robot! Copy NCLab, Inc 2017 all s reserved.