CS 1301 Review Keith OHara keith oharagatech edu

Programming Jargon § Value - fundamental programming quantity with a type § § Float

Expressions § Code snippets that evaluate to some value. § § § § Sep

Types of Values § Integers (like integers in math) § -1, -2, 300000, 0

Have Type-Sense § Your expressions should make sense in terms of what type they

Order of Operations § Order an expression is evaluated § PEMDAS § § Parentheses

Variables § Variables refer to values § § b = 3 + 2 a

Statements § Code snippets that do stuff! § Driving the robot § forward(1, 0.

Useful Functions § A function is a piece of code you can use over

Using Simple Functions § Functions that interact with the robot § forward (speed) §

Writing Simple Functions § Defining functions § Creates function § Does not execute/run them

Writing Simple Functions def function-name(): statement … statement name() Sep 3 2007 CS 1301

Writing Functions with Parameters def nudge(speed): print “Going forward with speed”, speed forward(speed) print

Octaves of A Do I need the parentheses around 2**octave? def beep. A(length, octave):

Writing Functions with Parameters def function-name(p 1, p 2, …, pn): statement … statement

Using Functions that Return Values name = raw_input(“Enter your name”) print “Hello”, name print

Converting between types § § § float(3000) int(3. 99999) str(3. 9) int(“ 3”) int(“

Composing Functions print abs(int(0 - 3. 5)) print abs(int(-3. 5)) print abs(-3) print 3

Writing Functions that Return Values def area(radius): return 3. 14 * radius**2 def circumference(diameter):

Functions with Local Variables def area(radius): a = 3. 14 * radius**2 return a

Variables in a Function are Local § Variables in a function are private §

Different Variables - Same Name def area(radius): a = 3. 14 * radius**2 return

Writing Functions with Return Values def function-name(list-of-params): statement … statement return value output =

Passing variables to functions userinput = raw_input(“Enter a number”) number = int(userinput) print “Absolute

Calling Your Own Functions def area(radius): return 3. 14 * radius**2 invalue = raw_input(“Enter

Calling Your Own Functions def rect_area(length, width): area = length*width return area l =

Same Name - Different Variables def rect_area(length, width): area = length*width return area length

Same Name - Different Variables def rect_area(length, width): area = length*width length = 0

Functions in general # description of this function # what it expects as input

Math Functions § Math module § Set of useful math functions Sep 3 2007

Where’s the Error? def avg. Light(): left = get. Light(‘left’) center = get. Light(‘center’)

Test on Friday Sep 3 2007 CS 1301 - O'Hara 37

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

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 Sep 3 2007 CS 1301 - O'Hara 2

Expressions § Code snippets that evaluate to some value. § § § § Sep 3 2007 3**2 #evaluates to 9 (3+2)*(4+2) 3. 0/2. 0 “hello” + “world” (3 == 4) #evals (3 != 4) #evals (3 < 4) #evals “abc” < “bcd” #evals CS 1301 - O'Hara to to False True 3

Types of Values § Integers (like integers in math) § -1, -2, 300000, 0 § Floating Points (like “decimals”) § -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 Sep 3 2007 CS 1301 - O'Hara 4

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] Sep 3 2007 CS 1301 - O'Hara 5

Order of Operations § Order an expression is evaluated § PEMDAS § § Parentheses Exponentiation Multiplication, Division Addition, Subtraction (3 -2)*(4+2)**2 (1) * (6)**2 (1) * (36) 36 § Left-to-Right Sep 3 2007 CS 1301 - O'Hara 6

Variables § Variables refer to values § § b = 3 + 2 a = b * 2 my. Name = “Keith” in. CS 1301 = True # b = 5 # a = 10 § “=“ 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 Sep 3 2007 CS 1301 - O'Hara 7

Statements § Code snippets that do stuff! § Driving the robot § forward(1, 0. 5) § stop § beep(1, 440) § Assignment § classname = “cs 1301” § Displaying to the screen § print classname § print “We love”, classname, “it’s great” Sep 3 2007 CS 1301 - O'Hara 8

Useful Functions § A function is a piece of code you can use over and over again input § 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) Sep 3 2007 CS 1301 - O'Hara function output 9

Using Simple Functions § Functions that interact with the robot § forward (speed) § beep(time, frequency) § Pass them arguments § Execute in sequential order forward(1) stop() beep(1, 440) § flow of execution § Top-level § not in any function Sep 3 2007 CS 1301 - O'Hara 10

Writing Simple Functions § Defining functions § Creates function § Does not execute/run them § Indenting implies “scope” or code ownership § Call functions from top-level or other functions Sep 3 2007 Indent def nudge(): print “going forward” forward(1) print “about to stop” stop() nudge() CS 1301 - O'Hara No Indention “Top Level” 11

Writing Simple Functions def function-name(): statement … statement name() Sep 3 2007 CS 1301 - O'Hara 12

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) Sep 3 2007 CS 1301 - O'Hara 13

Octaves of A Do I need the parentheses around 2**octave? def beep. A(length, octave): beep(length, 27. 5 * (2**octave)) beep. A(1, 4) beep. A(1, 1) beep. A(3, 6) Sep 3 2007 # A 4 # A 5 # A 6 § § CS 1301 - O'Hara A 4 : 440 Hz A 5: 880 Hz A 6: 1760 Hz A 7: 3520 Hz 14

Writing Functions with Parameters def function-name(p 1, p 2, …, pn): statement … statement function-name(v 1, v 2, …, vn) Sep 3 2007 CS 1301 - O'Hara 15

Using Functions that Return Values name = raw_input(“Enter your name”) print “Hello”, name print “Robot battery voltage”, get. Battery() p = take. Picture() show(p) v = abs(-3) print “Absolute value of (-3) =“, v Sep 3 2007 CS 1301 - O'Hara 16

Converting between types § § § float(3000) int(3. 99999) str(3. 9) int(“ 3”) int(“ 3. 0”) Sep 3 2007 # # # returns returns error CS 1301 - O'Hara 3000. 0 3 3 ‘ 3. 9’ ‘ 3’ 17

Composing Functions print abs(int(0 - 3. 5)) print abs(int(-3. 5)) print abs(-3) print 3 show(take. Picture()) n = int(raw_input(“Enter a number”)) n = int(“ 9”) n = 9 Sep 3 2007 CS 1301 - O'Hara 18

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) Sep 3 2007 CS 1301 - O'Hara 19

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) Sep 3 2007 CS 1301 - O'Hara 20

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 Sep 3 2007 CS 1301 - O'Hara 21

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 Sep 3 2007 CS 1301 - O'Hara 22

Writing Functions with Return Values def function-name(list-of-params): statement … statement return value output = function-name(list-of-params) Sep 3 2007 CS 1301 - O'Hara 23

Passing variables to functions userinput = raw_input(“Enter a number”) number = int(userinput) print “Absolute value = “, abs(number) Sep 3 2007 CS 1301 - O'Hara 24

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) Sep 3 2007 CS 1301 - O'Hara 25

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) Sep 3 2007 CS 1301 - O'Hara 26

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) Sep 3 2007 CS 1301 - O'Hara 27

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 Sep 3 2007 CS 1301 - O'Hara 28

Functions in general # description of this function # what it expects as input # what is provides as output def function (p 0, p 2, …, pn): statement … statement return value z = function(a 0, a 2, …, an) Sep 3 2007 CS 1301 - O'Hara 29

Math Functions § Math module § Set of useful math functions Sep 3 2007 CS 1301 - O'Hara § import math § math. sin(math. pi) § math. log(100) 30

Where’s the Error? def avg. Light(): left = get. Light(‘left’) center = get. Light(‘center’) right = get. Light(‘right’) avg = (left + center + right) / 3. 0 print “Average Light Reading: ”, avg. Light() § Forgot to return the value! Sep 3 2007 CS 1301 - O'Hara 31

Where’s the Error? def avg. Light(): left = get. Light(‘left’) center = get. Light(‘center’) right = get. Light(‘right’) avg = (left + center + right) / 3. 0 return avg print “Average Light Reading: ”, avg. Light() § No Indentation Sep 3 2007 CS 1301 - O'Hara 32

Where’s the Error? def avg. Light(): left = get. Light(‘left’) center = get. Light(‘center’) right = get. Light(‘right’) avg = (left + center + right) / 3. 0 return avg. Light() print “Average Light Reading: ”, avg § avg is a local variable to the avg. Light function Sep 3 2007 CS 1301 - O'Hara 34

Where’s the Error? def avg. Light(): left = get. Light(‘left’) center = get. Light(‘center’) right = get. Light(‘right’) avg = left + center + right / 3. 0 return avg print “Average Light Reading: ”, avg. Light() § Order of Operations wrong! Sep 3 2007 CS 1301 - O'Hara 35

Where’s the Error? def avg. Light(): left = get. Light(‘left’) center = get. Light(‘center’) right = get. Light(‘right’) avg = (left + center + right) / 3 return avg print “Average Light Reading: ”, avg. Light() § Integer Division Sep 3 2007 CS 1301 - O'Hara 36

Test on Friday Sep 3 2007 CS 1301 - O'Hara 37