How Do Robots Find Their Way?

Transcription

1 How Do Robots Find Their Way? Conditionals and Repetition

2

3

4 Learning Objectives Learn basic programming concepts (variables, if statements, loops, and functions) and write simple programs using these concepts.

5 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

6 Robots are dumb What does a robot need to know how to do to solve a maze? What commands and behaviors would be useful?

7

8

9 Can I move forward?

10 If these is empty space, then move forward

11 If these is empty space, then move forward Conditional

12 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

13 It is raining Wear a raincoat

14 Grade is at least 50 Pass the class

15 There is empty space in front of the robot The robot moves forward

16 True or false, aka Boolean value There is empty space in front of the robot The robot moves forward

17 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

18 and Everything has to be true

19 and true and true = true true and false and true = false false and false = false

20 or Only one thing has to be true

21 or true or true = true true or false or true = true false or false = false

22 What will the result of this expression be? (true and (not false) or (true and not false))

23 What will the result of this expression be? ((not false) or (false and (not true)) and false)

24 What will the result of this expression be? ((not false) or (false and (not true)) and false)

25 Using the logic at right, suppose our robot decides to pivot left. Which of the following can be true? (a) (b) (c) There is a wall only behind the robot and to its left. There is a wall only behind the robot. There is a wall to the left and right of the robot, but not in front. if (wall on left) and (no wall on right) and (no wall on front): then pivot right otherwise: pivot left Text : a 90277: b 90279: c

26 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

27 Anything that results in true or false can go into the if part of a conditional

28 I am buying a movie ticket and I am a student I will get a discount on the price

29 My percentage is at least 77 and my percentage is at most 79 My grade is B+

30 The battery is dead or there is no gas The car will not start

31 Not married and not engaged and like it Put a ring on it

32 Boolean Expressions in Python Type the following into the shell: 5 == 5

33 Boolean Expressions in Python Type the following into the shell: 5 == 5 Equality Operator

34 Boolean Expressions in Python Type the following into the shell: 5 == 4

35 Boolean Expressions in Python Type the following into the shell: 5!= 4

36 Boolean Expressions in Python Type the following into the shell: 5!= 4 Inequality Operator

37 If-Statements in Python Type the following into the shell: if 5 == 5: print(1)

38 If-Statements in Python Here is the syntax for if-statements in Python: if <a Boolean expression>: <code to run if the Boolean expression is true>

39 If-Statements in Python Here is the syntax for if-statements in Python: Something that must be either true or false if <a Boolean expression>: <code to run if the Boolean expression is true>

40 If-Statements in Python Here is the syntax for if-statements in Python: "Then" after this we must if <a Boolean expression>: indent <code to run if the Boolean expression is true>

41 If-Statements in Python Here is the syntax for if-statements in Python: if <a Boolean expression>: <code to run if the Boolean expression is true> Indentation tells Python how much code is part of the "then"

42 If-Statements in Python Here is the syntax for if-statements in Python: if <a Boolean expression>: <code to run if the Boolean expression is true> Everything with the same indentation will run when the Boolean expression is true

43 If-Statements in Python What will get printed here (if anything)? if 7 > 6 and (3 > 4 or 4 < 5): print(1)

44 If-Else Statements in Python Here is the syntax for if-else statements in Python: if <a Boolean expression>: <code to run if Boolean expression is true> else: <code to run if the Boolean expression is false>

45 If-Else Statements in Python Here is the syntax for if-else statements in Python: if <a Boolean expression>: <code to run if Boolean expression is true> else: "Otherwise" <code to run if the Boolean expression is false>

46 What is the output? x = 25 if x < 15: if x > 8: print(1) else: print(2) else: print(3) Text : : : : : : 2 3

47 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

48 How would you find your way out of a maze?

49 Right-Hand Rule Same idea, but with left hand:

50 One Move with Right-Hand Rule 1. If there is empty space to my right, then pivot right and step forward. 2. Otherwise, if there is empty space in front of me, then step forward. 3. Otherwise, if there is empty space to my left, then pivot left and step forward. 4. Otherwise pivot right without stepping forward.

51

52

53 There is a wall, so no

54 No wall in front, so yes!

55

56 There is a wall, so no

57 There is a wall, so no

58 No wall to the left, so yes!

59

60

61 Maze Solving in Python Remember, functions (aka routines) can "return" results!

62 Maze Solving in Python Suppose these functions existed in Python, and returned Boolean values: emptyspacetoright() emptyspacetoleft() emptyspaceinfront()

63 Maze Solving in Python Suppose these functions existed in Python, and simply caused the robot to take the associated action: pivotleft() pivotright() stepforward()

64 Maze Solving in Python Then one step in maze-solving would look like this: if emptyspacetoright(): pivotright() stepforward() elif emptyspaceinfront(): stepforward() elif emptyspacetoleft(): pivotleft() stepforward() else: pivotright()

65 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

66

67 How many times do I move before I m out of the maze??

68 Instead: I ll just keep moving until I get out

69 Loops Drive the same track multiple times: each lap is exactly the same

70 while loop Drive the track while the race is not over

71 while not at exit, continue making moves

72 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

73 While Loops in Python while <Boolean value>: <loop body>

74 While Loops in Python while <Boolean value>: <loop body> While loop: Drive around the track...

75 While Loops in Python while <Boolean value>: <loop body>...running this code again on every lap around the track...

76 While Loops in Python while <Boolean value>: <loop body>...until this Boolean is no longer true

77 While Loops in Python while <Boolean value>: <loop body> And yes, the colon the indentation are still important!

78 Example x = 0 while x < 2: x = x + 1 print(x)

79 Example x is given a value of 0 x = 0 while x < 2: x = x + 1 print(x)

80 Example The Boolean expression is checked x = 0 while x < 2: x = x + 1 print(x)

81 Example x = 0 while x < 2: x = x + 1 print(x) 1 is added to x, so x is now 1

82 Example x = 0 while x < 2: x = x + 1 print(x) 1 is printed to the shell

83 Example x = 0 while x < 2: x = x + 1 print(x) Lap one is now finished

84 Example x = 0 while x < 2: x = x + 1 print(x) so check the Boolean expression again

85 Example x = 0 while x < 2: x = x + 1 print(x) x becomes 2

86 Example x = 0 while x < 2: x = x + 1 print(x) 2 is printed to the shell

87 Example x = 0 while x < 2: x = x + 1 print(x) Lap two is now finished

88 Example x = 0 while x < 2: x = x + 1 print(x) so check the Boolean expression again Now that x is 2, the expression is false, and we're done!

89 What is the output? x = 6 while x > 4: print(x) x = x - 1 Text : : : : :

90 What is the output? n = 3 while n > 0: if n == 5: n = -99 print(n) n = n + 1 Text : : : :

91 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving

92 What does "driving a lap" mean in the context of robot maze solving?

93 Maze Solving Logic 1. while I have not reached the exit: 1. If there is empty space to my right, then pivot right and step forward. 2. Otherwise, if there is empty space in front of me, then step forward. 3. Otherwise, if there is empty space to my left, then pivot left and step forward. 4. Otherwise pivot right without stepping forward.

94 Maze Solving in Python Suppose that in addition to our previous functions, the following was also defined in Python: reachedexit()

95 Maze Solving in Python Then our whole maze-solving logic would look like this: while not reachedexit(): if emptyspacetoright(): pivotright() stepforward() elif emptyspaceinfront(): stepforward() elif emptyspacetoleft(): pivotleft() stepforward() else: pivotright()

96 Part 1 Robot behavior Conditionals Logic More complex conditionals Maze solving Part 2 Repeating behaviour While loops Loops in Maze Solving