CS101Autumn 2019

7/30/19 Autumn 2019 CS101@CSE IIT Bombay

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CS 101Computer Programming

and UtilizationPuruwith

several CS101 TAs and CSE staff

Course webpage: http://www.cse.iitb.ac.in/~cs101/

Lecture 1: Introduction

Clip art and quote credits: Various sources found through Google Image Search

abouttheseslides

• basedonChapter1ofthebook– AnIntroductiontoProgrammingthroughC++byProf.AbhiramRanade(TataMcGrawHill,2014)

• originalslidesbyAbhiram Ranade– updatesandcontributionsbyVarsha Apte,Uday Khedker,Sunita Sarawagi,Umesh Bellur,OmDamani,GaneshRamakrishnan

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Autumn 2019 CS101@CSE IIT Bombay

somequestions

• whyacomputer?

• whatisacomputer?

• whatisprogramming?

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whycomputer?

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Autumn 2019 CS101@CSE IIT Bombay

whycomputer?

• yetanotheroptiononthehuman-machineaxis• automationfordoingwork

– efficiently,quickly,newdiscoveries/explanationsetc.

• thecomputer– amachineintheautomationworldthathasinfluencedalmostallaspectsofourexistence

– hassomepropertiesunique/differentfromothermachines

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Autumn 2019 CS101@CSE IIT Bombay

whatisuniqueaboutacomputer?

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vs.

what is a computer?

• computer:amachinethatcando(specified)work– …thatcancompute

• compute:perform(elaborate)calculations– combinationofmathematicalandlogicaloperations

• acomputer– isanelectronicdevicewithcomplexcircuitry– isaprogrammable device

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a computercandomanythings

Help book and manage tickets Store and search documents

Help design physical systems: say water networkWeather prediction

Autumn 2019 CS101@CSE IIT Bombay

all of us have already used a computer!

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– Calculator– ATM– Smartphone

(is a computer)

Autumn 2019 CS101@CSE IIT Bombay

howtodoworkwithacomputer?

• tellitdowork!

• whatwork?andhowtospecify?

whatwork=>logic,calculations,sequenceetc.

howtospecify=>writeaprogramusingaprogramminglanguage

• thiscourse: fromuserstoprogrammers!

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CS101assessment/grading

• Midtermexam:~20%• 2Quizzes:~10%each• Finalexam:~30%• Labsessions

– Labtests:~20%weightage– Labattendance:~10%weightage

• MandatorytoattendN-1outofNlabs• Everylabsubsequentlymissedwillcost2%

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• Lectureslots(SectionS1)Slot11Tuesdays3:30PM– 5:00PM&Fridays3:30PM– 5:00PM(SectionS2)Slot5Wed9:30AM– 11:00AM&Fridays9:30AM– 11:00AM

• LabsessionsTuesdays,WednesdaysandThursdays8PMuntil11PMinSL1,SL2andBasementlab(newCSE building)

• Slidesandvideosonwww.cse.iitb.ac.in/~cs101 andhttp://bodhitree2019.cse.iitb.ac.in

CS101 schedule/logisticshttps://www.cse.iitb.ac.in/~cs101/

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The TA treeCTA

STA

JTAs

Tue lab.batch

STA

JTAs

Wed lab.batch

STA

JTAs

Bodhitree/Web siteLab scheduling

Do not use personal email

Thu lab.batch

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additional help for CS101

• do not hesitate in contacting us if are facing problem due to English

• आप अंग्रेजीकेकारणसमस्याकासामनाकररहेहैंतोहमसेसंपकर् करनेमेंसंकोचनकरें

• there will be one Teaching Assistant for every ~12 students– Help and support can provided in other languages

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let’sstartprogramming!

• whatisaprogram?– logic/concept/idea/calculations…– sequenceofinstructions(thatacomputercanunderstand)thatcapturethelogic

• wealreadydothis…– whichroutetotaketoreachLA001?– whattimetowakeupforclass?– howtobookanola/uber ride?– howtoprepareforanexam?– …

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programs

• program =aprecisedescriptionofthecalculationswewantthecomputertoperform

• byfeedingdifferentprogramstoacomputeryoucanmakeitdodifferentcalculations

• thiscoursetellsyouhowtoconstruct(“write”)programs• specialnotationistobeusedtowriteprograms:“ProgrammingLanguage”(C++forthiscourse)

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goal for today

• writesomesmallprogramsusingC++programminglanguage

• theprogramswilldrawpicturesonthescreen• we“drive”a“turtle”onthescreen!

• Turtle hasapen,soitdrawsasitmoves• drawingpicturesmayseembefun,butifyoumasterit,youhavemasteredalotofprogramming

• willusesimplecpp packagedevelopedbyProf. AbhiramRanade,basedonLogo

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programming the turtle to draw

instructions the turtle understands• forward (x): Move forward x pixels

– E.g. forward(50) moves the turtle forward 50 pixels• right (x): turn right by x degrees• left(x): turn left by x degrees • penUp()

– Will not draw while moving• penDown()

– Will draw while moving

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programming a turtle to draw a square

• forward, right, left, penUp, penDown

• With these instructions, make the turtle move in such a way that we will draw a square of length 200

• What facts do we need to know before we can program?

• Note: By default, in the beginning, the turtle faces towards the east, and the pen is down

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The square drawing program

#include <simplecpp>

main_program { turtleSim();forward(200); right(90);forward(200); right (90);forward(200); right(90);forward(200);

}

The square drawing program

#include <simplecpp>

main_program { turtleSim();forward(200); right(90);forward(200); right (90);forward(200); right(90);forward(200);

}

Some magic abracadabra: ignorethe program will use the simplecpp package.

Your commands within these braces {..}.

Start the turtle simulator (open a window)

Move forward 200 units

Turn right 90 degrees

Program exits

General Ideas

#include<simplecpp>

main_program{

turtleSim();

forward(200); right(90);

forward(200); right(90);

forward(200); right(90);

forward(200);wait(10);

}

This sequence of commands in C++ is the program

Commands or statementsterminated by semicolon ";"

Some commands need additional information called arguments• 90 is the argument to the

command right• 200 is the argument to the

command forward

General Ideas (contd)

#include<simplecpp>

main_program{turtleSim();forward(200);right(90);forward(200);right(90);forward(200);right(90);forward(200);wait(10);}

Commands are generally executed from top to bottom, left to right.

how to draw an octagon?

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how to draw an octagon?

• commands seem quite repetitive?

• there is a better way!

#include<simplecpp>main_program{

turtleSim();forward(100);right(45);forward(100);right(45);forward(100);right(45);forward(100);right(45);forward(100);right(45);forward(100);right(45);forward(100);right(45);forward(100);right(45);

wait(10);}

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A Better Way

#include <simplecpp>

main_program{turtleSim(); repeat(8){

forward(100); right(45);

}}

repeat (n) {

some commands

}

The instructions within {...} are repeated n times

Each round of execution is called an iteration

How to Draw a Polygon?

#include <simplecpp>

main_program{turtleSim(); repeat(8){

forward(100); right(45);

}}

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How to Draw a Polygon?

#include <simplecpp>

main_program{turtleSim();

repeat(num_sides){forward(10); right(360.0/num_sides);

} }

#include <simplecpp>

main_program{turtleSim();

repeat(8){forward(10); right(45);

} }

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How to Draw a Polygon?

#include <simplecpp>

main_program{turtleSim();

int num_sides;

repeat(num_sides){forward(10); right(360.0/num_sides);

} }

We need some magic so that num_sides can have the right value

Tell the computer: Reserve space in your memory where I can store an integer (int). I will refer to it by the name num_sides

Divide the number 360 by the number stored in the space named num_sides and pass the result as an argument to this command

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Explanation#include <simplecpp>main_program{

turtleSim();

int num_sides;

cout << “No. of sides?”;cin >> num_sides;

repeat(num_sides) {forward(200);right(360.0/num_sides);

}}

Print the sentence within the quotes on the screencout è “Console out” (display)

Read the number that the user types and store it into the space in memory named num_sides cin ç “Console in” (keyboard)

Use the integer stored in the space in memory which is namednum_sides

Formatting: Indentation, Grouping, Naming

#include <simplecpp>

main_program{turtleSim();int num_sides;

cout << “No. of sides?”;cin >> num_sides;

repeat(num_sides) {forward(200);right(360.0/num_sides);

}}

#include <simplecpp>main_program{turtleSim();cout << “No. of sides?”;int n;cin >> n;repeat(n) {forward(200);right(360.0/n);}}

You will lose marks for bad formatting

Can we improve the program further?main_program{

turtleSim();int num_sides;

cout << “No. of sides?”;cin >> num_sides;

repeat(num_sides) {forward(200);right(360.0/num_sides);

}}

main_program{turtleSim();

int num_sides; int side_length = 200;double exterior_angle;

cout << “No. of sides?”;cin >> num_sides;

exterior_angle = 360.0/num_sides;

repeat(num_sides) {forward(side_length);right(exterior_angle);

}}

Can we improve the program further?Both values for a polygon,

number of sides andside length

are user inputs.

int num_sides; int side_length;double exterior_angle;double sum_exterior = 360;

cout << “No. of sides?”;cin >> num_sides;

cout << “Side length?”;cin >> side_length;

exterior_angle = sum_exterior/num_sides;

repeat(num_sides) {forward(side_length);right(exterior_angle);

}}

language syntax

• syntax =grammatical rulesindicatinghowcommandsmustbewritten

• syntaxofprogramminglanguagesisverystrict,e.g.– “right(90);”cannotbewrittenas“right90;”.– “penUp()”cannotbewrittenas“penup()”oreven“penUp”,i.e.withoutparentheses.

– wewilllaterlearnotherkindsofstatementswhichwillhavetheirownsyntaxwhichmustbeadheredto.

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Nested Repeat Statements

It will draw a square with dashed lines

repeat(4){

repeat(3){

forward(50); penUp();

forward(50); penDown();

}

right(90);

}

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what does the following program do?

#include <simplecpp>

main_program{cout << “a”;repeat(5){

cout << “b”;repeat(2){ cout << “c”; }cout << “d”;

}}

what does the following program do?

#include <simplecpp>

main_program{cout << “a”;repeat(5){

cout << “b”;repeat(2){ cout << “c”; }cout << “d”;

}}

abccdbccdbccdbccdbccd

curly braces group statements

repeat(4){

forward(50); right(90);wait(2);

}

repeat(4)

forward(50); right(90);wait(2);

repeat(4){

forward(50);}right(90);wait(2);

more commands/functions

• sqrt(x) : square root of x

• trigonometric functions,

• x is in radian: sin(x), cos(x), tan(x)

• x is in degree sine(x), cosine(x), tangent(x)

• also for arcsine, arccosine, arctangent etc.

compile and execute this program

1. Raise one of your hands2. Put down your raised hand3. Close your eyes and count loudly up to 104. Loudly say ‘Ha Ha Ha’5. Write the value of Pi ( π ) correct to 3 decimal places6. Loudly say “Thank you” in your mother tongue7. Clap three times8. While executing this program, ignore all earlier

instructions and just raise both hands

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running/executing the program

• Compiling a program: translating it into a form that a computer can understand

• the result of compilation: an executable file

• compiler used by us is called s++

running a program on computer

• Type in an editor (say, gedit)• Save the file (say prog.cpp)• Compile (s++ prog.cpp)• It generates a binary file a.out• Execute (./a.out )

• Note that in case compilation fails with some error, existing a.out file is untouched

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The Spirit of The Course

LearnC++statements/conceptsLearnhowtoexpressproblemsyouwanttosolveusingC++

Goal:ifyoucansolveaproblembyhand,possiblytakinganenormousamountoftime,bytheendofthecourse,youshouldbeabletowriteaprogramforit

Learnnewwaysofsolvingproblems!

How to master the course

• Do not be afraid of using the computer

• “What if I write xyz in my program instead of pqr?”

Just do so and find out

• Be adventurous.

• But first write your logic on paper, think about how the computer will execute your instructions, and only then type them up

Why Picture Drawing?

• Picture drawing requires calculatione.g. 360.0/num_sides

• “Draw a triangle with sides of lengths 3, 4, 5 units”

You will need to do trigonometric calculations to find out the angles between the sides

• More interesting calculations will be needed to draw more interesting drawings

A pattern with 36 repetitions. You know enough to write a program to do this! Try it.

End of Lecture

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Compilation and execution summary

CPU RAM Disk Keyboard Display

Operating system (Windows, Linux, Mac OS, …)

C/C++ execution environment

Bashshellio

stre

am

mat

h

strin

g

main() function in a.out

char, short, int, float, double, if, switch, while, …

Source code prog.cpp

iostreammath.hstring

Prec

ompi

led

libra

ries

Head

erfile

s

s++ compiler

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PC building blocks: motherboard

CPU withcooling fan

Magneticdisk dataconnectors

Fastelectronicmemory

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Storage and peripheral devices

Rotatingmagneticplatters

Record/playhead on arm

Data cable betweendisk and motherboard

KeyboardDisplay

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CPU

Simplified abstract viewArithmetic

and logic unit

Register 0Register 1Register 2

…

Random accessmemory (RAM)

RAM location 0RAM location 1RAM location 2

…Address

Data Reserved fordisplay

Reserved for keyboard

Program that tells the CPU what to do and

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