CS 101

(1)

CS101

Autumn 2019

(2)

CS 101

Computer Programming and Utilization

Puru with

several CS101 TAs and CSE staff

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

Lecture 1: Introduction

(3)

about these slides

• based on Chapter 1 of the book

– An Introduction to Programming through C++

by Prof. Abhiram Ranade (Tata McGraw Hill, 2014)

• original slides by Abhiram Ranade

– updates and contributions by

Varsha Apte, Uday Khedker, Sunita Sarawagi,

Umesh Bellur, Om Damani, Ganesh Ramakrishnan

(4)

some questions

• why a computer?

• what is a computer?

• what is programming?

(5)

why computer?

(6)

why computer?

• yet another option on the human-machine axis

• automation for doing work

– efficiently, quickly, new discoveries/explanations etc.

• the computer

– a machine in the automation world that has influenced almost all aspects of our existence

– has some properties unique/different from other machines

(7)

what is unique about a computer?

vs.

(8)

what is a computer?

• computer: a machine that can do (specified) work

– … that can compute

• compute: perform (elaborate) calculations

– combination of mathematical and logical operations

• a computer

– is an electronic device with complex circuitry – is a programmable device

(9)

a computer can do many things

Help book and manage tickets Store and search documents

(10)

all of us have already used a computer!

– Calculator – ATM

– Smartphone (is a computer)

(11)

how to do work with a computer?

• tell it do work!

• what work? and how to specify?

what work => logic, calculations, sequence etc.

how to specify => write a program using a programming language

• this course: from users to programmers!

(12)

CS101 assessment/grading

• Midterm exam: ~20%

• 2 Quizzes: ~10% each

• Final exam: ~30%

• Lab sessions

– Lab tests: ~20% weightage

– Lab attendance: ~10% weightage

• Mandatory to attend N-1 out of N labs

• Every lab subsequently missed will cost 2%

(13)

• Lecture slots

(Section S1) Slot 11

Tuesdays 3:30 PM – 5:00 PM & Fridays 3:30 PM – 5:00 PM (Section S2) Slot 5

Wed 9:30 AM – 11:00 AM & Fridays 9:30 AM – 11:00 AM

• Lab sessions

Tuesdays, Wednesdays and Thursdays 8 PM until 11 PM in SL1, SL2 and Basement lab (newCSE building)

• Slides and videos on

www.cse.iitb.ac.in/~cs101 and http://bodhitree2019.cse.iitb.ac.in

CS101 schedule/logistics

https://www.cse.iitb.ac.in/~cs101/

(14)

The TA tree

CTA STA

JTAs

Tue lab.

batch

STA

JTAs

Wed lab.

batch

STA

JTAs

Bodhitree/Web site Lab scheduling

Do not use personal email Thu lab.

batch

(15)

additional help for CS101

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

• आप अंग्रेजी के कारण समस्या का सामना कर रहे हैं तो हमसे संपकर्

करने में संकोच न करें

• there will be one Teaching Assistant for every ~12 students

– Help and support can provided in other languages

(16)

(17)

let’s start programming!

• what is a program?

– logic/concept/idea/calculations …

– sequence of instructions (that a computer can understand) that capture the logic

• we already do this …

– which route to take to reach LA001?

– what time to wake up for class?

– how to book an ola/uber ride?

– how to prepare for an exam?

– …

(18)

programs

• program = a precise description of the calculations we want the computer to perform

• by feeding different programs to a computer you can make it do different calculations

• this course tells you how to construct (“write”) programs

• special notation is to be used to write programs:

“Programming Language”(C++ for this course)

(19)

goal for today

• write some small programs using C++ programming language

• the programs will draw pictures on the screen

• we “drive” a “turtle” on the screen!

• Turtle has a pen, so it draws as it moves

• drawing pictures may seem be fun, but if you master it, you have mastered a lot of programming

• will use simplecpp package developed by Prof. Abhiram

Ranade, based on Logo

(20)

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

(21)

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

(22)

The square drawing program

#include <simplecpp>

main_program { turtleSim();

forward(200); right(90);

forward(200); right (90);

forward(200);

}

(23)

The square drawing program

main_program { turtleSim();

forward(200); right (90);

forward(200);

}

Some magic abracadabra: ignore the 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

(24)

General Ideas

#include<simplecpp>

main_program{

turtleSim();

forward(200);

wait(10);

}

This sequence of commands in C++ is the program

Commands or statements terminated by semicolon ";"

Some commands need

additional information called arguments

• 90 is the argument to the command right

(25)

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.

(26)

how to draw an octagon?

(27)

how to draw an octagon?

• commands seem quite repetitive?

• there is a better way!

main_program{

turtleSim();

wait(10);

}

(28)

A Better Way

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

(29)

How to Draw a Polygon?

main_program{

turtleSim();

repeat(8){

forward(100);

right(45);

} }

(30)

How to Draw a Polygon?

main_program{

turtleSim();

repeat(num_sides){

forward(10);

right(360.0/num_sides);

} }

main_program{

turtleSim();

repeat(8){

forward(10);

right(45);

} }

(31)

How to Draw a Polygon?

main_program{

turtleSim();

int num_sides;

repeat(num_sides){

forward(10);

} }

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

(32)

Explanation

main_program{

turtleSim();

int num_sides;

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

repeat(num_sides) { forward(200);

} }

Print the sentence within the quotes on the screen

cout 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 named

(33)

Formatting: Indentation, Grouping, Naming

main_program{

turtleSim();

int num_sides;

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

}

main_program{

turtleSim();

cout << “No. of sides?”; int n;

cin >> n;

repeat(n) { forward(200);

right(360.0/n);

} }

(34)

Can we improve the program further?

main_program{

turtleSim();

int num_sides;

} }

main_program{

turtleSim();

int num_sides;

int side_length = 200;

double exterior_angle;

exterior_angle = 360.0/num_sides;

repeat(num_sides) {

forward(side_length);

right(exterior_angle);

(35)

Can we improve the program further?

Both values for a polygon, number of sides and

side length

are user inputs.

int num_sides;

int side_length;

double exterior_angle;

double sum_exterior = 360;

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

exterior_angle =

sum_exterior/num_sides;

repeat(num_sides) {

forward(side_length);

right(exterior_angle);

(36)

language syntax

• syntax = grammatical rules indicating how commands must be written

• syntax of programming languages is very strict, e.g.

– “right(90);” cannot be written as “right 90;”.

– “penUp()” cannot be written as “penup()” or even “penUp”, i.e. without parentheses.

– we will later learn other kinds of statements which will have their own syntax which must be adhered to.

(37)

Nested Repeat Statements

It will draw a

square with dashed lines

repeat(4){

repeat(3){

forward(50); penUp();

forward(50); penDown();

}

right(90);

}

(38)

what does the following program do?

main_program{

cout << “a”; repeat(5){

cout << “b”;

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

} }

(39)

what does the following program do?

main_program{

cout << “a”; repeat(5){

cout << “b”;

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

} }

(40)

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);

(41)

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.

(42)

compile and execute this program

1. Raise one of your hands 2. Put down your raised hand

3. Close your eyes and count loudly up to 10 4. Loudly say ‘Ha Ha Ha’

5. Write the value of Pi ( π ) correct to 3 decimal places 6. Loudly say “Thank you” in your mother tongue

7. Clap three times

8. While executing this program, ignore all earlier instructions and just raise both hands

(43)

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++

(44)

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

(45)

The Spirit of The Course

Learn C++ statements/concepts

Learn how to express problems you want to solve using C++

Goal: if you can solve a problem by hand, possibly

taking an enormous amount of time, by the end of the course, you should be able to write a program for it

Learn new ways of solving problems!

(46)

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

(47)

Why Picture Drawing?

• Picture drawing requires calculation e.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

(48)

A pattern with 36 repetitions. You know

enough to write a program to do this! Try it.

(49)

End of Lecture

(50)

Compilation and execution summary

Operating system (Windows, Linux, Mac OS, …) C/C++ execution environment

Bash shell

iostream

math

string

main() function in a.out char, short, int, float,

double, if, switch, while, …

Source code prog.cpp

iostream math.h

string

mpiled rariesHeader files s++ compiler

(51)

PC building blocks: motherboard

CPU with cooling fan

Magnetic disk data

Fast

electronic memory

(52)

Storage and peripheral devices

Rotating magnetic platters

Record/play

Keyboard Display

(53)

CPU

Simplified abstract view

Arithmetic and logic unit

Register 0 Register 1 Register 2

…

Random access memory (RAM) RAM location 0 RAM location 1 RAM location 2

… Address

Data Reserved for display

Reserved for keyboard

Program that tells the CPU what to do and