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CS 1301 Review

CS 1301 Review. Keith O’Hara keith.ohara@gatech.edu. http://wiki.roboteducation.org. 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

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CS 1301 Review

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

  2. 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 CS1301 - O'Hara

  3. 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 CS1301 - O'Hara

  4. 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 CS1301 - O'Hara

  5. 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] CS1301 - O'Hara

  6. 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 CS1301 - O'Hara

  7. 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 CS1301 - O'Hara

  8. 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” CS1301 - O'Hara

  9. 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) input function output CS1301 - O'Hara

  10. 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 CS1301 - O'Hara

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

  12. Writing Simple Functions def function-name(): statement statement … statement name() CS1301 - O'Hara

  13. 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) CS1301 - O'Hara

  14. Octaves of A Do I need the parentheses around 2**octave? 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 CS1301 - O'Hara

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

  16. 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 CS1301 - O'Hara

  17. 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 CS1301 - O'Hara

  18. 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 CS1301 - O'Hara

  19. 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) CS1301 - O'Hara

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

  21. 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 CS1301 - O'Hara

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

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

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

  25. 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) CS1301 - O'Hara

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

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

  28. 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 CS1301 - O'Hara

  29. Functions in general # description of this function # what it expects as input # what is provides as output def function (p0, p2, …, pn): statement … statement return value z = function(a0, a2, …, an) CS1301 - O'Hara

  30. Math Functions • import math • math.sin(math.pi) • math.log(100) • Math module • Set of useful math functions CS1301 - O'Hara

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

  32. 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() • No Indentation CS1301 - O'Hara

  33. 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(1) • Not calling function correctly CS1301 - O'Hara

  34. Where’s the Error? 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 • avg is a local variable to the avgLight function CS1301 - O'Hara

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

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

  37. Test on Friday CS1301 - O'Hara

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