CSci 127: Introduction to Computer Science

hunter.cuny.edu/csci

This lecture will be recorded

CSci 127 (Hunter) Lecture 5 6 October 2020 1 / 31

Frequently Asked Questions

From email

Can we do more on colors, images, numpy & matplotlib?Yes, we will in Labs 6-9 & Lectures 6-9.Today, we’ll focus on decisions, and logical expressions & circuits.

What is pseudocode? Why do we use it?Pseudocode is the “informal high-level description of the operating principle of acomputer program or other algorithm.”We use it to write down the ideas, before getting deep into the details.

What are types of variables?Different kinds of information takes different amounts of space.Types we have seen so far: int, float, str and objects (e.g. turtles).

How can I tell strings from variables?Strings are surrounded by quotes (either single or double).Variables names (identifiers) for memory locations are not. Ex: ’num’ vs. num.

How can I tell if I am on track?You should have submitted programs 1-20. This week we will work on programs21-25.If you are not working on programs the week of the related lab you will likelyfall behind. Submitting at the due date should be for emergency only!!!

From email

Can we do more on colors, images, numpy & matplotlib?

Yes, we will in Labs 6-9 & Lectures 6-9.Today, we’ll focus on decisions, and logical expressions & circuits.

From email

What is pseudocode? Why do we use it?

Pseudocode is the “informal high-level description of the operating principle of acomputer program or other algorithm.”We use it to write down the ideas, before getting deep into the details.

From email

What is pseudocode? Why do we use it?Pseudocode is the “informal high-level description of the operating principle of acomputer program or other algorithm.”

We use it to write down the ideas, before getting deep into the details.

From email

What are types of variables?

Different kinds of information takes different amounts of space.Types we have seen so far: int, float, str and objects (e.g. turtles).

From email

How can I tell strings from variables?

Strings are surrounded by quotes (either single or double).Variables names (identifiers) for memory locations are not. Ex: ’num’ vs. num.

From email

How can I tell strings from variables?Strings are surrounded by quotes (either single or double).

Variables names (identifiers) for memory locations are not. Ex: ’num’ vs. num.

From email

How can I tell strings from variables?Strings are surrounded by quotes (either single or double).Variables names (identifiers) for memory locations are not.

Ex: ’num’ vs. num.

From email

How can I tell if I am on track?

You should have submitted programs 1-20. This week we will work on programs21-25.If you are not working on programs the week of the related lab you will likelyfall behind. Submitting at the due date should be for emergency only!!!

From email

How can I tell if I am on track?You should have submitted programs 1-20. This week we will work on programs21-25.

If you are not working on programs the week of the related lab you will likelyfall behind. Submitting at the due date should be for emergency only!!!

From email

Today’s Topics

Recap: Decisions

Logical Expressions

Circuits

Binary Numbers

Today’s Topics

Recap: Decisions

Logical Expressions

Circuits

Binary Numbers

Challenge

Some challenges with types & decisions:

Python Tutor

(Demo with pythonTutor)

Decisions

(programiz)

Side Note: Reading Flow Charts

(xkcd/518)

Today’s Topics

Recap: Decisions

Logical Expressions

Circuits

Binary Numbers

Challenge

Predict what the code will do:

Python Tutor

Logical Operators

in1 in2 returns:False and False False

False and True False

True and False False

True and True True

in1 in2 returns:False or False False

False or True True

True or False True

True or True True

in1 returns:not False True

not True False

Logical Operators

True and True True

False or True True

True or False True

True or True True

not True False

Logical Operators

True and True True

False or True True

True or False True

True or True True

not True False

ChallengePredict what the code will do:

Python Tutor

Today’s Topics

Recap: Decisions

Logical Expressions

Circuits

Binary Numbers

Circuit Demo

(Demo with circuitverse)

Challenge

Predict when these expressions are true:

• in1 or not in1:

• not(in1 or in2):

• (in1 and in2) and in3:

Circuit Demo

Challenge

Draw a circuit that corresponds to each logical expression:

in1 or in2

(in1 or in2) and (in1 or in3)

(not(in1 and not in2)) or (in1 and (in2 and in3))

Circuit Demo

Today’s Topics

Recap: Decisions

Logical Expressions

Circuits

Binary Numbers

Logic → Circuits → Numbers

Digital logic design allows for two states:I True / FalseI On / Off (two voltage levels)I 1 / 0

Computers store numbers using the Binary system (base 2)

A bit (binary digit) being 1 (on) or 0 (off)

Binary Numbers

Digital logic design allows for two states:

I True / FalseI On / Off (two voltage levels)I 1 / 0

Binary Numbers

Digital logic design allows for two states:I True / False

I On / Off (two voltage levels)I 1 / 0

Binary Numbers

Digital logic design allows for two states:I True / FalseI On / Off (two voltage levels)

I 1 / 0

Binary Numbers

Two digits: 0 and 1

Each position is a power of twoI Decimal: the ”ones”, ”tens”, ”hundreds” and so on (powers of 10)I Binary: the ”ones”, ”twos”, ”fours”, ”sixteens” and so on (powers of 2)

In each position the digit is either 0 or 1, so given a binary number wecan obtain the decimal equivalent as follows:

I In the ”ones” position we either have a 1 or notI In the ”twos” position we either have a 2 or notI In the ”fours” position we either have a 4 or not ...

Example:11001base2 = 16 + 8 + 1 = 25base10

Binary Numbers

Two digits: 0 and 1

Each position is a power of two

I Decimal: the ”ones”, ”tens”, ”hundreds” and so on (powers of 10)I Binary: the ”ones”, ”twos”, ”fours”, ”sixteens” and so on (powers of 2)

Binary Numbers

Two digits: 0 and 1

Each position is a power of twoI Decimal: the ”ones”, ”tens”, ”hundreds” and so on (powers of 10)

I Binary: the ”ones”, ”twos”, ”fours”, ”sixteens” and so on (powers of 2)

Binary Numbers

Two digits: 0 and 1

Binary Numbers

Two digits: 0 and 1

Binary Numbers

Two digits: 0 and 1

I In the ”ones” position we either have a 1 or not

I In the ”twos” position we either have a 2 or notI In the ”fours” position we either have a 4 or not ...

Binary Numbers

Two digits: 0 and 1

I In the ”ones” position we either have a 1 or notI In the ”twos” position we either have a 2 or not

I In the ”fours” position we either have a 4 or not ...

Binary Numbers

Two digits: 0 and 1

Binary Numbers

Two digits: 0 and 1

Lecture Quiz

Log-in to Gradescope

Find LECTURE 5 Quiz

Take the quiz

You have 3 minutes

Challenge: Tech Interview Classic

Write a program that prints the numbers from 1 to 100. But formultiples of three print “Fizz” instead of the number and for themultiples of five print “Buzz”. For numbers which are multiples ofboth three and five print “FizzBuzz”.

Write down the output to see the pattern:12Fizz4BuzzFizz7...14FizzBuzz

Write the algorithm then, if time, write the code.

Write down the output to see the pattern:

12Fizz4BuzzFizz7...14FizzBuzz

Write down the output to see the pattern:1

2Fizz4BuzzFizz7...14FizzBuzz

Write down the output to see the pattern:12

Fizz4BuzzFizz7...14FizzBuzz

Write down the output to see the pattern:12Fizz

4BuzzFizz7...14FizzBuzz

Write down the output to see the pattern:12Fizz4

BuzzFizz7...14FizzBuzz

Write down the output to see the pattern:12Fizz4Buzz

Fizz7...14FizzBuzz

Write down the output to see the pattern:12Fizz4BuzzFizz

7...14FizzBuzz

Write down the output to see the pattern:12Fizz4BuzzFizz7

...14FizzBuzz

Write down the output to see the pattern:12Fizz4BuzzFizz7...14

FizzBuzz

Tech Interview Classic

To Do List:I Create a loop that goes from 1 to 100.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I If divisible by both, print “FizzBuzz”.I Otherwise print the number.

Order matters!!! To print FizzBuzz when i is divisible by both it shouldbe checked first, otherwise it will never get to this case!

To Do List:

I Create a loop that goes from 1 to 100.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I If divisible by both, print “FizzBuzz”.I Otherwise print the number.

To Do List:I Create a loop that goes from 1 to 100.

I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I If divisible by both, print “FizzBuzz”.I Otherwise print the number.

To Do List:I Create a loop that goes from 1 to 100.I If the number is divisible by 3, print “Fizz”.

I If the number is divisible by 5, print “Buzz”.I If divisible by both, print “FizzBuzz”.I Otherwise print the number.

To Do List:I Create a loop that goes from 1 to 100.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.

I If divisible by both, print “FizzBuzz”.I Otherwise print the number.

To Do List:I Create a loop that goes from 1 to 100.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I If divisible by both, print “FizzBuzz”.

I Otherwise print the number.Order matters!!! To print FizzBuzz when i is divisible by both it shouldbe checked first, otherwise it will never get to this case!

To Do List (Reordered):

I Create a loop that goes from 1 to 100.I If divisible by both 3 and 5, print “FizzBuzz”.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I Otherwise print the number.I Also should print a new line (so each entry is on its own line).

To Do List (Reordered):I Create a loop that goes from 1 to 100.I If divisible by both 3 and 5, print “FizzBuzz”.

I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I Otherwise print the number.I Also should print a new line (so each entry is on its own line).

To Do List (Reordered):I Create a loop that goes from 1 to 100.I If divisible by both 3 and 5, print “FizzBuzz”.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I Otherwise print the number.I Also should print a new line (so each entry is on its own line).

To Do List:I Create a loop that goes from 1 to 100.I If divisible by both 3 and 5, print “FizzBuzz”.I If the number is divisible by 3, print “Fizz”.I If the number is divisible by 5, print “Buzz”.I Otherwise print the number.I Also should print a new line (so each entry is on its own line).

for i in range(1,101):

if i%3 == 0 and i%5 == 0:

print("FizzBuzz")

elif i%3 == 0:

print("Fizz")

elif i%5 == 0:

print("Buzz")

print(i)

if i%3 == 0 and i%5 == 0:

print("FizzBuzz")

elif i%3 == 0:

print("Fizz")

elif i%5 == 0:

print("Buzz")

print(i)

if i%3 == 0 and i%5 == 0:

print("FizzBuzz")

elif i%3 == 0:

print("Fizz")

elif i%5 == 0:

print("Buzz")

print(i)

if i%3 == 0 and i%5 == 0:

print("FizzBuzz")

elif i%3 == 0:

print("Fizz")

elif i%5 == 0:

print("Buzz")

print(i)

if i%3 == 0 and i%5 == 0:

print("FizzBuzz")

elif i%3 == 0:

print("Fizz")

elif i%5 == 0:

print("Buzz")

print(i)

if i%3 == 0 and i%5 == 0:

print("FizzBuzz")

elif i%3 == 0:

print("Fizz")

elif i%5 == 0:

print("Buzz")

print(i)

In Python, we introduced:

I DecisionsI Logical ExpressionsI CircuitsI Binary Numbers

In Python, we introduced:

I DecisionsI Logical ExpressionsI CircuitsI Binary Numbers

Practice Quiz & Final Questions

Since you must pass the final exam to pass the course, we end everylecture with final exam review.

Pull out something to write on (not to be turned in).

Lightning rounds:I write as much you can for 60 seconds;I followed by answer; andI repeat.

Past exams are on the webpage (under Final Exam Information).

We’re starting with Spring 2018, Version 1.

Lightning rounds:

I write as much you can for 60 seconds;I followed by answer; andI repeat.

Lightning rounds:I write as much you can for 60 seconds;

I followed by answer; andI repeat.

Lightning rounds:I write as much you can for 60 seconds;I followed by answer; and

I repeat.

See you next week!

Before next lecture, don’t forget to:

Work on this week’s Online Lab

Optional - attend live Lab Review on Wednesday 1-2:30pm

Take the Lab Quiz on Gradescope by 6pm on Wednesday

Submit this week’s 5 programming assignments (programs 21-25)

At any point, visit our Drop-In Tutoring if you need help!!!

CSci 127: Introduction to Computer Science · CSci 127 (Hunter) Lecture 5 6 October 20202/31....

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