CS 101 Computer Programming and Utilization Puru with several - - PowerPoint PPT Presentation

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CS 101 Computer Programming and Utilization Puru with several - - PowerPoint PPT Presentation

Feb 09, 2023 244 likes •771 views

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

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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

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

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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

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Autumn 2019 CS101@CSE IIT Bombay

some questions

  • why a computer?
  • what is a computer?
  • what is programming?

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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

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what is unique about a computer?

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vs.

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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

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a computer can do many things

Help book and manage tickets Store and search documents Help design physical systems: say water network Weather prediction

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all of us have already used a computer!

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– Calculator – ATM – Smartphone (is a computer)

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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!

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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%

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  • 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/

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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

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additional help for CS101

  • do not hesitate in contacting us if are facing

problem due to English

  • आप अंग्ऱेजी क

े कारण समस्रा का सामना कर रहे हैः तो हमसे संपक रॎ करने मेः संकोच न करेः

  • there will be one Teaching Assistant for every ~12

students

– Help and support can provided in other languages

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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? – …

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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)

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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

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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); }

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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); }

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

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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 statements terminated 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

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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.

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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

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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

  • n 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 num_sides

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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

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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); }

}

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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 << “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); }

}

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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.

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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”; } }

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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”; } }

abccdbccdbccdbccdbccd

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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);

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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.
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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

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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++
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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

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!

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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

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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

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

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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 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 Precompiled libraries Header files s++ compiler

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PC building blocks: motherboard

CPU with cooling fan Magnetic disk data connectors Fast electronic memory

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Storage and peripheral devices

Rotating magnetic platters Record/play head on arm Data cable between disk and motherboard Keyboard Display

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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 how to do it

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