sep 3 2007cs1301 - o'hara1 cs 1301 review keith o’hara [email protected]

Sep 3 2007 CS1301 - O'Hara 1

CS 1301

Review

CS 1301

ReviewKeith O’[email protected]

http://wiki.roboteducation.org

Sep 3 2007 CS1301 - O'Hara 2

Programming JargonProgramming 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 CS1301 - O'Hara 3

ExpressionsExpressions

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

Sep 3 2007 CS1301 - O'Hara 4

Types of ValuesTypes 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

Sep 3 2007 CS1301 - O'Hara 5

Have Type-SenseHave 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 CS1301 - O'Hara 6

Order of OperationsOrder 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

Sep 3 2007 CS1301 - O'Hara 7

VariablesVariables

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 bx = x +1

Sep 3 2007 CS1301 - O'Hara 8

StatementsStatements

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”

Sep 3 2007 CS1301 - O'Hara 9

Useful FunctionsUseful 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

Sep 3 2007 CS1301 - O'Hara 10

Using Simple FunctionsUsing 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

Sep 3 2007 CS1301 - O'Hara 11

Writing Simple FunctionsWriting Simple Functions

def nudge():

print “going forward”

forward(1)

print “about to stop”

stop()

nudge()

Indent

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”

Sep 3 2007 CS1301 - O'Hara 12

Writing Simple FunctionsWriting Simple Functionsdef function-name():

statement

statement

…

statement

name()

Sep 3 2007 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)

Sep 3 2007 CS1301 - O'Hara 14

Octaves of AOctaves of A

def beepA(length, octave):beep(length, 27.5 * (2**octave))

beepA(1,4) # A4beepA(1,1) # A5beepA(3,6) # A6 A4 : 440 Hz

A5: 880 Hz A6: 1760 Hz A7: 3520 Hz

Do I need the parentheses

around 2**octave?

Sep 3 2007 CS1301 - O'Hara 15



def function-name(p1, p2, …, pn):

statement

statement

…

statement

function-name(v1, v2, …, vn)

Sep 3 2007 CS1301 - O'Hara 16

Using Functions that Return Values

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

Sep 3 2007 CS1301 - O'Hara 17

Converting between typesConverting 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

Sep 3 2007 CS1301 - O'Hara 18

Composing Functions 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

Sep 3 2007 CS1301 - O'Hara 19

Writing Functions that Return ValuesWriting 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 CS1301 - O'Hara 20

Functions with Local Variables Functions with Local Variables

def area(radius):a = 3.14 * radius**2return a

def circumference(diameter):c = 3.14 * diameterreturn c

print “Area of a 3 ft circle”, area(3)print “Circumference”, circumference(2*3)

Sep 3 2007 CS1301 - O'Hara 21

Variables in a Function are Local

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 CS1301 - O'Hara 22

Different Variables - Same Name

Different Variables - Same Name

def area(radius):a = 3.14 * radius**2return a

def circumference(radius):a = 3.14 * 2 * radiusreturn a

print “Area of a 3 ft circle”, area(3)print “Circumference”, circumference(3)print a

Sep 3 2007 CS1301 - O'Hara 23

Writing Functions with Return Values

Writing Functions with Return Values

def function-name(list-of-params):

statement

statement

…

statement

return value

output = function-name(list-of-params)

Sep 3 2007 CS1301 - O'Hara 24

Passing variables to functionsPassing variables to functions

userinput = raw_input(“Enter a number”)

number = int(userinput)

print “Absolute value = “, abs(number)

Sep 3 2007 CS1301 - O'Hara 25

Calling Your Own FunctionsCalling 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 CS1301 - O'Hara 26

Calling Your Own FunctionsCalling 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 CS1301 - O'Hara 27

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 CS1301 - O'Hara 28



def rect_area(length, width):area = length*widthlength = 0width = 0return area

length = int(raw_input(“Enter the length”))width = int(raw_input(“Enter the width”)) area = rect_area(length, width)print “The rectangle length =”, lengthprint “The rectangle width =”, widthprint “The rectangle area =”, area

Sep 3 2007 CS1301 - O'Hara 29

Functions in generalFunctions 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)

Sep 3 2007 CS1301 - O'Hara 30

Math FunctionsMath Functions

import math math.sin(math.pi) math.log(100)

Math module Set of useful math

functions

Sep 3 2007 CS1301 - O'Hara 31

Where’s the Error?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()

Sep 3 2007 CS1301 - O'Hara 32


No Indentation


avg = (left + center + right) / 3.0return avg


Sep 3 2007 CS1301 - O'Hara 33


Not calling function correctly



print “Average Light Reading:”, avgLight(1)

Sep 3 2007 CS1301 - O'Hara 34


avg is a local variable to the avgLight function



avgLight()print “Average Light Reading:”, avg

Sep 3 2007 CS1301 - O'Hara 35

Where’s the Error?Where’s the Error?def avgLight():

left = getLight(‘left’)center = getLight(‘center’)right = getLight(‘right’)

avg = left + center + right / 3.0

return avg


Order of Operations wrong!

Sep 3 2007 CS1301 - O'Hara 36

Where’s the Error?Where’s the Error?def avgLight():

left = getLight(‘left’)center = getLight(‘center’)right = getLight(‘right’)

avg = (left + center + right) / 3

return avg


Integer Division

Sep 3 2007 CS1301 - O'Hara 37

Test on FridayTest on Friday

sep 3 2007cs1301 - o'hara1 cs 1301 review keith o’hara [email protected]

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