grapefruit print("grapefruit") C. grapefruit else: - - - PowerPoint PPT Presentation

Practicum 2: Conditionals, For Loops, etc

What is the output of the given code?

• A. orange
• B. orange

grapefruit

• C. grapefruit
• D. grapefruit

lemon

• E. lemon

x = 12 if x > 10: print("orange") elif x > 0: print("grapefruit") else: print("lemon")

we'll start in

a few

mins !

←

⇒

→

• xouihftexs#to

Logical Expressions

• why "==" and not "=" to test for equality?
• A. python is just trying to be tricky
• B. "==" will test to see if two values are the same and "=" will test to see if the

values stored in two variables are the same

• C. the premise of this question is wrong—you can use "=" to test for equality
• D. "=" is has a different meaning in python code

5=-5

X==5

s

• S

x

• S

x Is

y

• Yg

yet

• O
• assignment operator

Logical Expressions

• What are the results of evaluating the following logical expressions?
• 5 != 7
• 13.2 > 6.6 and 6.6 < 3
• 13.2 > 6.6 or 6.6 < 3
• 'a' == 'apple'
• 'a' < 'g'
• 'A' < 'g'
• D True

(

T

)

(

F

) → False

T

F

→ True

• D False

{

→ True

• b tent out
• n your
• wn !

Conditionals: in "pseudocode"

• We want to write a program that:
• asks the user for a number
• if the number is larger than 1000, tell them that they picked a big

number

• when the program finishes, displays a message telling the user that the

program is done

⑦

e,

if

2)

3)

Conditionals: in "pseudocode"

• We want to write a program that:
• asks the user for a number
• if the number is larger than 1000, tell them that they picked a big

number

• otherwise, tells them that they did not pick a big number
• when the program finishes, displays a message telling the user that the

program is done

iflela

:

3

4

Conditionals: in "pseudocode"

ask the user for a number tell them that it's big tell them that the program has finished running tell them that it's not big

else

Conditionals

• We incorporate logical expressions into code with conditionals (also called "selection

statements")

• Our first example of a conditional is an "if" statement
• All conditionals evaluate logical expressions to a boolean value (True or False)

if logical expression: # code to run if the logical expression # evaluates to True # notice indent!

T

Conditionals

• If we want to run certain code in one case and other code in all other cases, we will you an "if/else"

statement

if logical expression: # code to run if the logical expression # evaluates to True # notice indent! else: # code to run if the logical expression # evaluates to False

O

⇐

Conditionals

• If we have more than two branches, we'll use an if/elif/else structure

if logical expression 1: # code to run if the logical expression 1 # evaluates to True # notice indent! elif logical expression 2: # code to run if the logical expression 1 evaluates to False # and logical expression 2 evaluates to True else: # code to run if the logical expression # evaluates to False

if

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• n:&

lot

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For Loops

• All loops are used to repeat code. We may want to do the same task over

and over, and we may want to do a very similar task over and over.

• Flip a coin 10 times
• Remind your roommate to do the dishes once for each dish left in the

sink

• Count from 1 to 100

For loops: in "pseudocode"

• We want to write a program that:
• asks the user for their age
• prints out "happy birthday" the same number of times as their age
• when the program finishes, displays a message telling the user that the

program is done

H

2) 3)

For loops: in "pseudocode"

ask the user for their age print out "happy birthday" tell them that the program has finished running

1)

2)

x the user's age

3)

For Loops

• For loops are used (as opposed to while loops) when we know ahead of

time how many times the loop needs to repeat:

for variable_name in something_we_can_loop_over: # code that we want repeated # code to run when we're done

times = 5 # I know now how many times to repeat for time_number in range(times): print("repetition!") print("all done!")

→ &

S

For Loops

• The number of times might be hardcoded, come from the user, be a

programmatically generated value, or be the length of a list (as a few examples)

times = int(input("times? ")) # I know now how many times to repeat for time_number in range(times): print("repetition!") print("all done!")

Eri

to investigate

: yhiatu.is

no

thebe!got

For loops

• How many times does the given for

loop run?

• A. 10
• B. 5
• C. 2
• D. -3

x = 10 y = -3 if x < 100 and y > 0: x = 5 elif x > 0 or y > 0: x = 2 for time_number in range(x): print("repetition!")

x D2

T

F

→

Practicum today

• You'll be working with random numbers today
• This is how we can simulate a wide variety of coin, dice, and card games!
• (you also won't know what value they have until you run your programs!)
• Fun facts about random numbers:
• Truly random numbers are surprisingly difficult for computers to generate
• the random module in python generates "pseudorandom" numbers
• It uses the current time of your computer as a starting "seed" number to

generate what appears to be a sequence of random numbers.

Practicum today

• We'll code up one of the problems together around 15 minutes before the

end of practicum today!

• Those of you who are remote—you'll be in breakout rooms. Anuj, Satya

and myself will be rotating between the rooms.

• Use the "ask for help" button if one of us isn't there and you need some

help

• Please choose one person to screen share in your breakout room. You'll

all submit code individually, but we want you to discuss the problems and work together.

• 1:10