Computer Programmingand Utilization

CS101 Spring 2012

Soumen Chakrabarti

with

CS101 TAs and Staff

CS101 2012.1

First steps

http://www.cse.iitb.ac.in/~cs101/ Fill out survey when survey link appears Find out your lab batch

Eighty percent of success is showing up.

Woody Allen

CS101 2012.1

Places and times Lectures (two sections)

• Slot 10: Tu, F 2—3:30• Slot 6: W, F 11—12:30

Labs (OSL)• Four evenings a week, plus one makeup

Tutorial• Depends on interest

M T W Th FS6 (160)

S10 (160)

(80)

Make-up lab

CS101 2012.1

“The management”

STA

JTAs

Instructor

STA

JTAs

Tue lab.batch

STA

JTAs

Wed lab.batch

STA

JTAs

STA

JTAs

Fri lab.batch

Web site STAs

Assignment STAs

cs101.iitb@gmail.com

cs101stas@cse.iitb.ac.in

cs101jtas@cse.iitb.ac.in

Do not use personal email

Make-up lab.

Thu lab.batch

CS101 2012.1

Assessment Midterm exam and quizzes

• Two to three exams• Total 25—35%

Final exam• 30—40%

Some lab. sessions will be graded• 15—20%

Project and viva• 5—10%

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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 view

Arithmeticand 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

how to do it

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Rules of the game A register or a RAM location can store

exactly one value at any time Writing into a register or RAM location (or

reading into it from the keyboard) destroys the earlier value

Outputting a register or RAM location to the display is done by copying to the area reserved for the display; this does not destroy the source value

Accessing any RAM location is equally fast

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“Assemblylanguage

programming”

E.g.: Centigrade and Fahrenheit C/5 = (F-32)/9 Painful to say “register 5” and “RAM location 43” so

we will use shorter names Load input F from keyboard into R0 Load 32 into R1 Store R0R1 in R2 Load 9 in R3 Divide R2 by R3 and store in R4 Load 5 in R5 Multiply R5 by R4 and store in R6 Output R6 to the display

Painful!

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High level programming language

Programmer need not keep mental map of which register and RAM location contain values of what symbolic variables

Compiler or interpreter automatically translates from above format to register and RAM location manipulations we saw

•Input F from keyboard•Set C to 5*(F-32)/9•Output C to display

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Saying it in C++

Some details omitted Save above source code to text file Compile source code to executable file Call executable from a shell command line

main() {

float fahrenheit;

cin >> fahrenheit;

float centigrade = 5*(fahrenheit-32)/9;

cout << centigrade;

}

Procedure name

Variable declaration

Arithmetic expression

Variable type

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Ha

The hardware-software stack

Hardware

Operating System (Linux)

Shell command line (bash)

Your C++ executable program

Your program accesses resources like CPU, keyboard,display, through the lower layers of system software

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C++: More detail

What is a procedure? What are data types? Where did cin and cout come from? Rules of writing arithmetic expressions

main() {

float fahrenheit;

cin >> fahrenheit;

float centigrade = 5*(fahrenheit-32)/9;

cout << centigrade;

}

Procedure name

Variable declaration

Arithmetic expression

Data type

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Procedure or function Encapsulates a piece of computation and

gives it a name• E.g. main is the default procedure that is run

when your program is executed from the shell

May accept input values stored in named variables• E.g. int max(int a, int b)

And return output value• E.g. max(-3, 2) should return 2

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Data types Computer memory is a 2d array of bits

• Eight columns (one byte or “B”)• Rows depends on how much memory you have;

“1 GB” means 1,073,741,824 rows• Hard disk is similar, only larger and slower

What programmers want• Integers, real numbers, complex numbers• Characters, strings of characters• Arrays, variable length lists, mappings• Windows, buttons, menus

Will study how many of these are represented in memory

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Choosing names C++ allows any sequence of characters A—

Z, a—z, 0—9, and underscore Not starting with a digit Up to some maximum number of characters old_style_variable_name newStyleVariableName (“camel case”) turbineRPM or turbineRpm?

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cin and cout “Console in” (keyboard) and “console out”

(display) These variables are not defined magically To use them, must prefix our C++ code with

instruction to include a header file like this:#include <iostream>

The operating system and compiler work together to let your code access the keyboard and display through cin and cout

Not quite…

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Namespaces We must write std::cin and std::cout Two different Ravi Vermas in hostels 2 and 5 To avoid confusion, write asH2::RaviVerma and H5::RaviVerma

Lets libraries written by different people avoid variable and function name clashes

std is the “standard” namespace within which C++ predefined variables and functions are provided

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The std namespace and using Tedious to type std:: in front of everything If you are not using too many namespaces

simultaneously, you can choose a default by saying

using namespace std;before using things defined inside std.

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First complete source code

At your shell, typeg++ cf.cc

Now run resulting file as./a.out

#include <iostream>using namespace std;main() { float fahrenheit; cin >> fahrenheit; float centigrade = 5*(fahrenheit-32)/9; cout << centigrade;} Save to file “cf.cc”

Executable a.out

g++ compiler

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Files cf.cc and a.out are files A file is a sequence of bytes These bytes can be interpreted differently

depending on the applications that read or write the files• cf.cc is a text file to be written by a programmer

and read by the C++ compiler• Any name ending in .cc or .cpp is ok• a.out is an executable file to be run from the

shell command line• You can rename this file as you wish

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Disk organization: Directories A directory is a container that can contain

files and other directories Files cannot contain directories Tree hierarchy of directories Root is “slash” / Full path written as/usr/bin/g++

/

home

cs101 you

usr

bin

g++bash

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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 cf.cc

iostream

math.h

string

Pre

com

pile

d lib

rarie

sH

eade

rfil

es

g++ compiler

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Visual programming: Turtle graphics “Turtle” holding pen Initially touching paper Turn through angle Move some distance Pen down, pen up

forward(100);left(90);forward(100);left(90);forward(100);left(90);forward(100);

Repititive and boring

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Blocks and loops Want to draw arbitrary regular polygons Input: numSides (number of sides) Repeat numSides times:

• Move through a fixed length, say 100 units• Turn anticlockwise by 360/numSides degrees

int numSides;cin >> numSides;repeat(numSides) { forward(100); left(360/numSides);}

(What will happen if360/numSides isfractional?)

Red text shows a block of instructions to be

executed in sequence

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1st lab session Familiarize with Linux desktop Open a terminal window, the bash shell Your home and other directories; files Running shell commands Using a text editor Typing a small C++ program Compiling it using g++ Running the resulting executable file