1. Sep 3 2007CS1301 - O'Hara1 CS 1301 Review Keith O’Hara keith.ohara@gatech.edu http://wiki.roboteducation.org

2. Sep 3 2007CS1301 - O'Hara2 Programming Jargon  Value - fundamental programming quantity with a type  Float - 3.0  Integer - 3  String - “3”, “Three”  Boolean - True, False  Expression - Evaluates to a value.  3 + 2 - 6 *8  Statement - segment of code python executes and does something  print 3 + 2  Variable - name that refers to a value  x = 3 + 2

3. Sep 3 2007CS1301 - O'Hara3 Expressions  Code snippets that evaluate to some value.  3**2 #evaluates to 9  (3+2)*(4+2)  3.0/2.0  “hello” + “world”  (3 == 4) #evals to False  (3 != 4) #evals to True  (3 < 4) #evals to True  “abc” < “bcd” #evals to True

4. Sep 3 2007CS1301 - O'Hara4 Types of Values  Integers (like integers in math)  -1, -2, 300000, 0  Floating Points (like “decimals”)  -1.5, 1.5, 3.1415, 1.0  Character (like symbol of an alphabet)  ‘a’, ‘b’, ‘c’, ‘z’  Strings (a string of characters)  “CS”, “1301”, “rocks”  Booleans (a truth value)  True or False

5. Sep 3 2007CS1301 - O'Hara5 Have Type-Sense  Your expressions should make sense in terms of what type they are  Some make perfect sense  3 + 4 = 7 [int + int = int]  Some expressions make no sense  “hello” + 4 [ string + int]  Some expressions make (uncommon) sense  4.0 + 3 [float + int]  4.0 + 3 = 7.0 [float + int = float]  “CS” * 3 = “CSCSCS” [string * int = string]

6. Sep 3 2007CS1301 - O'Hara6 Order of Operations  Order an expression is evaluated  PEMDAS  Parentheses  Exponentiation  Multiplication, Division  Addition, Subtraction  Left-to-Right (3-2)*(4+2)**2 (1)*(4+2)**2 (1) * (6)**2 (1) * (36) 36

7. Sep 3 2007CS1301 - O'Hara7 Variables  Variables refer to values  b = 3 + 2 # b = 5  a = b * 2 # a = 10  myName = “Keith”  inCS1301 = True  “=“ means assignment not equality  b = 3 + 2 # store 5 in the variable b  b = 3 * 2 # store 6 in the variable b x = x +1

8. Sep 3 2007CS1301 - O'Hara8 Statements  Code snippets that do stuff!  Driving the robot  forward(1, 0.5)  stop  beep(1, 440)  Assignment  classname = “cs1301”  Displaying to the screen  print classname  print “We love”, classname, “it’s great”

9. Sep 3 2007CS1301 - O'Hara9 Useful Functions  A function is a piece of code you can use over and over again  Treat it like a black box  You pass it values, it does some work, and it returns values  You “call it”,”invoke it”, or “use it” by using its name and parentheses  The things you pass it go inside the parentheses  output = function(input) function input output

10. Sep 3 2007CS1301 - O'Hara10 Using Simple Functions forward(1) stop() beep(1, 440)  Functions that interact with the robot  forward (speed)  beep(time, frequency)  Pass them arguments  Execute in sequential order  flow of execution  Top-level  not in any function

11. Sep 3 2007CS1301 - O'Hara11 Writing Simple Functions def nudge(): print “going forward” forward(1) print “about to stop” stop() nudge() Inden t  Defining functions  Creates function  Does not execute/run them  Indenting implies “scope” or code ownership  Call functions from top-level or other functions No Indention “Top Level”

12. Sep 3 2007CS1301 - O'Hara12 Writing Simple Functions def function-name(): statement … name()

13. Sep 3 2007CS1301 - O'Hara13 Writing Functions with Parameters def nudge(speed): print “Going forward with speed”, speed forward(speed) print “About to stop” stop() nudge(.2) nudge(.9) nudge(1)

14. Sep 3 2007CS1301 - O'Hara14 Octaves of A def beepA(length, octave): beep(length, 27.5 * (2**octave)) beepA(1,4) # A4 beepA(1,1) # A5 beepA(3,6) # A6  A4 : 440 Hz  A5: 880 Hz  A6: 1760 Hz  A7: 3520 Hz Do I need the parentheses around 2**octave ?

15. Sep 3 2007CS1301 - O'Hara15 Writing Functions with Parameters def function-name(p1, p2, …, pn): statement … function-name(v1, v2, …, vn)

16. Sep 3 2007CS1301 - O'Hara16 Using Functions that Return Values name = raw_input(“Enter your name”) print “Hello”, name print “Robot battery voltage”, getBattery() p = takePicture() show(p) v = abs(-3) print “Absolute value of (-3) =“, v

17. Sep 3 2007CS1301 - O'Hara17 Converting between types  float(3000) # returns 3000.0  int(3.0) # returns 3  int(3.99999) # returns 3  str(3.9) # returns ‘3.9’  int(“3”) # returns ‘3’  int(“3.0”) # error

18. Sep 3 2007CS1301 - O'Hara18 Composing Functions print abs(int(0 - 3.5))  print abs(int(-3.5))  print abs(-3)  print 3 show(takePicture()) n = int(raw_input(“Enter a number”))  n = int(“9”)  n = 9

19. Sep 3 2007CS1301 - O'Hara19 Writing Functions that Return Values def area(radius): return 3.14 * radius**2 def circumference(diameter): return 3.14 * diameter print “Area of a 3 ft circle”, area(3) print “Circumference”, circumference(2*3)

20. Sep 3 2007CS1301 - O'Hara20 Functions with Local Variables def area(radius): a = 3.14 * radius**2 return a def circumference(diameter): c = 3.14 * diameter return c print “Area of a 3 ft circle”, area(3) print “Circumference”, circumference(2*3)

21. Sep 3 2007CS1301 - O'Hara21 Variables in a Function are Local  Variables in a function are private  Including the parameters  Each function has its own variables  Even when the names are the same  Allows you to write functions independently without worry about using the same name

22. Sep 3 2007CS1301 - O'Hara22 Different Variables - Same Name def area(radius): a = 3.14 * radius**2 return a def circumference(radius): a = 3.14 * 2 * radius return a print “Area of a 3 ft circle”, area(3) print “Circumference”, circumference(3) print a

23. Sep 3 2007CS1301 - O'Hara23 Writing Functions with Return Values def function-name(list-of-params): statement … return value output = function-name(list-of-params)

24. Sep 3 2007CS1301 - O'Hara24 Passing variables to functions userinput = raw_input(“Enter a number”) number = int(userinput) print “Absolute value = “, abs(number)

25. Sep 3 2007CS1301 - O'Hara25 Calling Your Own Functions def area(radius): return 3.14 * radius**2 invalue = raw_input(“Enter the radius”) r = int(invalue) Print “Area of a”, r, “ft circle”, area(r)

26. Sep 3 2007CS1301 - O'Hara26 Calling Your Own Functions def rect_area(length, width): area = length*width return area l = int(raw_input(“Enter the length”)) w = int(raw_input(“Enter the width”)) print “Area of rectangle”, rect_area(l,w)

27. Sep 3 2007CS1301 - O'Hara27 Same Name - Different Variables def rect_area(length, width): area = length*width return area length = int(raw_input(“Enter the length”)) width = int(raw_input(“Enter the width”)) print “Area of rect”, rect_area(length, width)

28. Sep 3 2007CS1301 - O'Hara28 Same Name - Different Variables def rect_area(length, width): area = length*width length = 0 width = 0 return area length = int(raw_input(“Enter the length”)) width = int(raw_input(“Enter the width”)) area = rect_area(length, width) print “The rectangle length =”, length print “The rectangle width =”, width print “The rectangle area =”, area

29. Sep 3 2007CS1301 - O'Hara29 Functions in general # description of this function # what it expects as input # what is provides as output def function (p 0, p 2, …, p n ): statement … return value z = function(a 0, a 2, …, a n )

30. Sep 3 2007CS1301 - O'Hara30 Math Functions  import math  math.sin(math.pi)  math.log(100)  Math module  Set of useful math functions

31. Sep 3 2007CS1301 - O'Hara31 Where’s the Error?  Forgot to return the value! def avgLight(): left = getLight(‘left’) center = getLight(‘center’) right = getLight(‘right’) avg = (left + center + right) / 3.0 print “Average Light Reading:”, avgLight()

32. Sep 3 2007CS1301 - O'Hara32 Where’s the Error?  No Indentation def avgLight(): left = getLight(‘left’) center = getLight(‘center’) right = getLight(‘right’) avg = (left + center + right) / 3.0 return avg print “Average Light Reading:”, avgLight()

33. Sep 3 2007CS1301 - O'Hara33 Where’s the Error?  Not calling function correctly def avgLight(): left = getLight(‘left’) center = getLight(‘center’) right = getLight(‘right’) avg = (left + center + right) / 3.0 return avg print “Average Light Reading:”, avgLight(1)

34. Sep 3 2007CS1301 - O'Hara34 Where’s the Error?  avg is a local variable to the avgLight function def avgLight(): left = getLight(‘left’) center = getLight(‘center’) right = getLight(‘right’) avg = (left + center + right) / 3.0 return avg avgLight() print “Average Light Reading:”, avg

35. Sep 3 2007CS1301 - O'Hara35 Where’s the Error? def avgLight(): left = getLight(‘left’) center = getLight(‘center’) right = getLight(‘right’) avg = left + center + right / 3.0 return avg print “Average Light Reading:”, avgLight()  Order of Operations wrong!

36. Sep 3 2007CS1301 - O'Hara36 Where’s the Error? def avgLight(): left = getLight(‘left’) center = getLight(‘center’) right = getLight(‘right’) avg = (left + center + right) / 3 return avg print “Average Light Reading:”, avgLight()  Integer Division

37. Sep 3 2007CS1301 - O'Hara37 Test on Friday