Boolean expressions, if statements, debugging, and …

What is in this lab?




    1. This lab bas 3 Tasks (3rd task has several parts). You should try to do these parts at home.



Task 2 and 3 are in the interactive textbook. Watch the video I provided (follow the link at page 7) before doing these two tasks.



2.  And 5 programming exercises (0 to 4)






The slides that are included here but do not explain either Tasks or Programming exercises are there as reminder of some relevant material that is needed for this lab.

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Lab 3 overview




    • Open a browser and log into Brightspace



    • On the left hand side under Labs tab, find lab3 material contained in either lab3-students.zip or lab3-studnets.pdf file



    • Download that file to the Desktop and open it.



    • Read slides one by one and follow the instructions explaining what to do. When stuck ask for help from TA. Ideally you should try to complete some, or all of this, at home and then use the lab as a place where you can get help with things you may have had difficulties with.


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Before starting, always make sure you are running Python 3



This slide is applicable to all labs, exercises, assignments … etc



ALWAYS MAKE SURE FIRST that you are running Python 3.4 (3.5 and 3.6 are fine too). That is, when you click on IDLE (or start python any other way) look at the first line that the Python shell displays. It should say Python 3.4 or 3.5 or 3.6 (and then some extra digits)



If you do not know how to do this, read the material provided with Lab 1. It explains it step by step







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div // and mod % operators in Python



If uncertain, here is how to compute a//b (i.e. integer division)
and a%b (i.e remainder)

1. Compute x=a/b

2. a//b is then equal to the whole (i.e integer) part of x. More precisely a//b is equal the integer that is closest to a/b but not bigger than a/b

3. a%b is equal to a - (a//b) * b














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Task 1

What is the type and value of each of the following expressions in Python? Do this in you head (and/or paper) first. The check both columns in Python shell. eg. You can test what kind of value the first expression returns by typing type(13*0.1) in Python shell

Expression
Type
Value



13 * 0.1
float
1.3



int(13) * 0.1


13 * int(0.1)


int(13 * 0.1)


13%7


6%3


6//2.5


6%2.5


2<3== 4<5




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Interactive textbook (Reminder)













Here is a link to the interactive textbook:



https://runestone.academy/runestone/static/thinkcspy/index.html






















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Task 2: Debugging





Follow this link, and read, run and do the exercises there:

https://runestone.academy/runestone/static/thinkcspy/Debugging/HowtoAvoidDebugging.html








An example used in the above link refers to the following problem from

Chapter: Simple Python Data, Section: Exercises, Question 3:
https://runestone.academy/runestone/static/thinkcspy/SimplePythonData/Exercises.html

Many people keep time using a 24 hour clock (11 is 11am and 23 is 11pm, 0 is midnight). If it is currently 13 and you set your alarm to go off in 50 hours, it will be 15 (3pm). Write a Python program to solve the general version of the above problem. Ask the user for the time now (in hours), and then ask for the number of hours to wait for the alarm. Your program should output what the time will be on the clock when the alarm goes off.



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Programming exercise 0:

More debugging and coding










Open file q0.py and solve the 3 programming exercises as instructed.























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Boolean Expressions


Boolean expressions evaluate to True or False



Logical/Boolean operators in Math and Python:

Math    Python

AND
and
OR
or
NOT
not


Here is how your compare two variables a and b in Math and Python

Math    Python

a = b

a ≤ b

a == b

a <= b

a ³ b
a ¹ b

a >= b

a != b
Truth table




A TRUTH TABLE for a compound Boolean expression shows

the results for all possible combinations of the simple expressions:

Testing if two strings are equal



For one of the programming exercise you will need to know that how to compare if two strings are equal. You can do that simply buy using == operator. Here are some examples

    • ‘A’==‘A’

True

    • ‘Anna’==‘Anna’

True

    • ‘Anna’=‘anna’ False

    • a=‘June’

    • a==‘june’ False

    • a==‘June’

True

    • b=‘Ju’ + ’ne’

    • a==b

True

ps. Do not copy paste the above into python shell. It will likely give you syntax

errors since quotes do not copy/paste correctly from Word.
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Examples of compound boolean expressions:

    • This is how you would test if age is at least 18 and at most 65:

age>=18 and age <= 65

    • not is an operator to negate the value of a simple or compound Boolean expression. Suppose age = 15. Then:
age > 16 evaluates to False, and not(age > 16) evaluates to True

    • Suppose day refers to a string which is a day of a week. Here is how you would test if day is a weekend:

day==“Saturday” or day==“Sunday”

    • Here are two ways to test if age is less than 18 and greater than 65. Think about the 2nd one

–  1st way:    age<18 and age > 65


–  2nd way:    not(age>=18 and age <= 65)

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Task 3: if statements

Follow all the links below. Read, run and do the exercises in each of them. No need to watch the videos.

Boolean Expressions
https://runestone.academy/runestone/static/thinkcspy/Selection/BooleanValuesandBooleanExpressions.html

Logical/Boolean operators

https://runestone.academy/runestone/static/thinkcspy/Selection/Logicaloperators.html

PrecedenceOfOperations

https://runestone.academy/runestone/static/thinkcspy/Selection/PrecedenceofOperators.html

Two-way if statement:

https://runestone.academy/runestone/static/thinkcspy/Selection/ConditionalExecutionBinarySelection.html


One-way if statement:

https://runestone.academy/runestone/static/thinkcspy/Selection/OmittingtheelseClauseUnarySelection.html


Nested if statement:

https://runestone.academy/runestone/static/thinkcspy/Selection/Nestedconditionals.html


Chained conditionals (i.e elif)

https://runestone.academy/runestone/static/thinkcspy/Selection/Chainedconditionals.html

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DOCSTRINGS





For all the python functions that you will write in the following questions (and in the future) make sure you document your functions by writing docstrings including the type contract (as we have done in class).




Test if you docstrings appear as help of your function by running help(your_function_name) in python shell.











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Programming exercises: Question 1


Write function called pay that takes as input an hourly wage and the number of hours an employee worked in the last week. The function should compute and return the employee’s pay. Overtime work should be paid in this way: Any hours beyond 40 but less than or equal 60 should be paid at 1.5 times the regular hourly wage. Any hours beyond 60 should be paid at 2 times the regular hourly wage. Important:


Important: Note that I did not give you either the number of parameters or the names of parameters. You will have to figure it out on your own for this function. Looking at the test examples below should help.




Example tests:


    • pay(10, 35)

350

    • pay(10, 45)

475.0

    • pay(10, 61)

720.0
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Programming exercises: Question 2



Rock, Paper, Scissors is a two-player game in which each player chooses one of three items. If both players choose the same item, the game is tied. Otherwise, the rules that determine the winner are:
(a)Rock always beats Scissors (Rock crushes Scissors)
    (b) Scissors always beats Paper (Scissors cut Paper)

    (c) Paper always beats Rock (Paper covers Rock)

Write a function called rps that takes the choice 'R', 'P', or ‘S' of player 1 and the choice of player 2, and returns −1 if player 1 wins, 1 if player 2 wins, or 0 if there is a tie.”

Note that I did not give you either the number of parameters or the names of parameters. You will have to figure it out on your own. Looking at the example runs below should help too:

Example tests:
    • rps('R', 'P')
1
    • rps('R', 'S')
-1
    • rps('S', 'S')
0

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Programming exercises: Question 3a




Open a new file with IDLE. Write a program that has a function called

is_divisible

    • The function is_divisible has two input parameters that are integers n and m and returns True if n is divisible by m and False otherwise.
    • Outside of that function, your program should interact with the user to get two integers. To determine if the 1st is divisible by the 2nd it should call is_divisible function. It should print a message explaining the result.


Two example tests (one on the left and one on the right)





>>>
>>>
Enter 1st integer:
Enter 1st integer:
9
8
Enter 2nd integer:
Enter 2nd integer:
3
3
9 is divisble by 3
8 is not divisble by 3 18
Programming exercises: Question 3b



Open a new file with IDLE. Write a program that has two functions one called is_divisible and the other called is_divisible23n8

•The function is_divisible is the same as in the previous questions so you can copy/paste it to the beginning of the new file.

•The function is_divisible23n8    has one input parameter, an integer.
It should return string “yes” if the given number is divisible by 2 or 3 but
not 8. Otherwise it should return a string “no”. Your function

is_divisible23n8 must use, i.e make a call to, is_divisible

•Outside of that function, your program should interact with the user to get one integer. It should call is_divisible23n8 function to deterimen if the number the user gave is divisible by 2 or 3 but not 8. It should print a message explaining the result.

>>>
an integer:
18

Enter



18 is
divisible by 2 or 3 but not 8
>>>
an integer:
16

Enter



It is
not true that 16 is divisible by 2 or 3 but not 8
>>>



Enter
an integer:
3
19
3 is divisible by
2
or 3 but not 8
Bonus programming exercises:



For those who are done and want to more programming exercises for the lab or home, follow this link and complete any, or ideally all, exercises there:




https://runestone.academy/runestone/static/thinkcspy/Selection/Exercises.html























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