summer school - facweb.iitkgp.ac.ingoutam/sss/lect/lect1.pdf · machine language program a nite...

Summer School Computer Sc & Engg: IIT Kharagpur 1'

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Summer School

�� on

�� Introduction to Programming

�� through

�� C and OCAML

Lect 1 Goutam Biswas


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�� Instructors

Goutam Biswas, Naveen Kumar Sharma, Sibasish

Dey, Shambhobi Bhattacharya, Arpita Routray�� Technical Support

Dr. D Roy, Alokesh Chattopadhyay, Mithun

Sarkar, B. P. Bandoghati, Dinanath Ghosh,

Debdash Bandyopadhyay, & Shibabroto Banerjee



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Computer System: An Overview



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VDU

Keyboard

ProcessorMemoryDisk etc.

Mouse

Network



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Primergy� ��

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� � � � � �

� � � � � �

� � � � � �



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CPU−Memory Bus

MMUDMA etc.

IO Bus

IO Controller

Disk II

IO Controller

IO Controller

CPU

Graphics VDU

Main Memory

Cache Memory

Disk I

Mouse

Network



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Types of Digital Computers

• General-purpose computers.

• Special-purpose computers - in washing

machine, refrigerator, music system, car,

mobile phone, camera, toy, instrument and

there is no end.



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Stored Program Computer

• A computer is used to process data.

• Computer cannot do anything on its own.

• It is given a sequence of instructions, called

a program, to process any data.

• Both program and data are stored in the

computer memory.



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Computer Models

von Neumann Model: A computer model whereboth data and program are stored in the samememory is called von Neumann architecturea

Harvard Model: Data and program are storedin different memory in the Harvardarchitectureb

aThe first draft of a report on the EDVAC at the Moore School of Electrical

Engineering, by John von Neuman, and the design of ENIAC by J. P. Eckert

and John W. Mauchly at the University of Pennsylvania.bHarvard Mark I electromechanical computer stored instructions on punched

tape and data in electro-mechanical counters.



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CPU Instruction Set

The set of instructions that the CPU of acomputer understands is called its machineinstructions.



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Machine Language Program

A finite sequence of machine instructions iscalled a machine language program. It is storedin the main memory for execution.



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Memory Location & Address

Program and data while execution are stored inthe main memory.Memory is divided into equal size blocksa calledmemory locations.Each memory location has a unique address.The CPU access a location by sending itsaddress to the memory subsystem.

aTypical size of each block is 1, 2, 4, or 8 bytes. One byte consists of eight

binary digit (8-bit).



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Program Execution

Fetch: The CPU fetches the next instructionfrom the memory and decodes (analyzes) it.

Execute: Action is taken according to therequirement of the instruction. It may benecessary to fetch data from the memory, or todo some arithmetic operation etc.

Continuation of this cycle is called programexecution.



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Central Processing Unit (CPU)



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Instruction Set

GPR File FPR File

Controller

FPUALU

PC IR PSW SP etc.



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Central Processing Unit (CPU)

• GPRs: general purpose registers

• FPRs: floating-point registers

• PC or IP: program counter or instruction

pointer

• PSW: program status word

• IR: instruction register



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Program and Data in the Main Memory

OtherProgram

OtherData

CPU

Data Bus

Address Bus

CPU−Memory Bus

Main Memory

MyData

MyProgram

OS



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Program Execution



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Instruction Fetch

The address of the next instruction is sent onthe address bus from a special register calledthe program counter (PC) or the instructionpointer (IP) of the CPU.



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Instruction Fetch

The content of the addressed location(instruction in this case) is read by the memorysubsystem and sent to the CPU on the databus.The CPU saves the instruction in a specialregister called instruction register (IR).



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Low Memory Address

CPU

PC

IR

Instruction Address

Instruction

Inst IInst II

Inst IIIInst IV

Inst XXXII

MyP

rogr

am

MyData

Main memory



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Instruction Decoding & Execution

Once the instruction is available in theinstruction register (IR), the CPU hardware(control circuit) decodes it, and takes asequence of actions. The action sequencedepends on the instruction.



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Data Fetch

If the instruction requires data from thememory, the CPU fetches it by sending theaddress of the dataa on the address bus.Memory subsystem sends the data on the databus.

aData address is already available in the CPU either as a part of the instruc-

tion (IR) or in some other CPU register.



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Data Fetch

The CPU may save the data in one of itsinternal registers and use it for the requiredoperation.



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Inst XXXII

CPU

DA

R Data Address

Data

Main memory

MyP

rogr

amM

yDat

aDR



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Result of an Instruction

The result of an instruction execution may be amodified data that may be stored in an internalregister of the CPU or in the memory.



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Memory Write

The CPU sends the address of the memorylocation and the data to write, on the addressand the data buses respectively. It also sends asignal for memory-write.



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With a Grain of Salt

�� The actual process is more complex



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A Machine Instruction of Pentium

�� 1000 0011 1110 1100 0000 1000

There is an internal register called esp in the

Pentium CPUa, that can store an integer value.

This instruction subtracts 8 from the data

stored in esp. �� esp ← esp - 8

aIt is a CPU and some more thing fabricated on silicon by Intel.



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Binary World

World inside a computer is mostly binary - itsalphabet has only two symbols 0 and 1.

But a language in binary may cause nightmareto human being.



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The Charge Of The Light Brigade

“Theirs not to make reply, Theirs not to reasonwhy, Theirs but to do & die”

The same text in binary inside a computerlooks as follows

01010100 01101000 01100101 0110100101110010 · · · · · · 00100000 01100100 0110100101100101 00001010



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Assembly Language Instruction

Machine language instructions are given a

human understandable symbolic representations

called assembly language instructions.�� 1000 0011 1110 1100 0000 1000 ⇒ sub 8, esp



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Assembly Language Program

A sequence of assembly language instructionsforms an assembly language program.



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Assembly Language to Machine Language

• The CPU does not understand assembly

language instructions.

• A program is written to translate an

assembly language program to the equivalent

machine language program.

• This program is known as assembler.



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High-Level Languages

It is also tedious to write “big programs” inassembly language.

Moreover an assembly language programcompletely depends on a particular CPU andthe computing environment.



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High-Level Languages

More human understandable programminglanguages were designed for the ease of writingprogram and also to make program moresystem independent. Following are the namesof a few such languages:Fortran, Basic, Lisp, Cobol, Algol, PL/I,Pascal, SML, Prolog, C, C++, Java, Haskell,OCAML, Ada, C#, Perl, Python, etc.



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Translation

A program in a high-level language cannotdirectly control the CPU. It is translated to anassembly language or a machine languageprogram.



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Translation

Two different types of translation schemes aregenerally used. One is called compilation andthe other is called interpretation.The software that translates a high-levelprogram to a machine language program iscalled a compiler. In an interpreter thetranslation and the execution goeshand-in-handa.

aSome high-level languages are more suitable for compilation and some other

languages are suitable for interpretation.



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Compiler: A Software Translator

HLL Program Machine Program

} {Translation Software



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Compiler: A Software Translator(cont.)

OtherProgramCPU

Data Bus

Address Bus

CPU−Memory Bus

Main Memory

OS

Compiler

Mach. Prog

HLL Prog



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Interpreter: A Software Translator

HLL Program

Translation

Execution Software

and



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Note

We shall see how a compiler translates a Cprogram and how an OCAML program isinterpreted.



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Writing and Storing a HLL Program

It is necessary to get some facility to write andstore a high-level language or an assemblylanguage program in a computer. This isprovided by a software called an editor e.g. vi,emacs etc.



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Writing and Storing a HLL Program

These softwares provide facility to edit a textand store it in the hard disk as a named objectcalled a file.



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int main()

KeyBoard

OS

Editor

HLL Prog

VDU

CPU

Address Bus

Data Bus

Main Memory

Disk

{

first.c



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Operating System

A computer system is very difficult to use unlessa master program called an operating system(OS) is running on it to make it user friendly.It provides a better view of the availableresources and it also manages resource.



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Operating System

We shall work on an OS called Linuxa.aThe initial version of this OS was designed by Linus Torvalds in 1991. But

in the current versions there is large contribution from GNU started by Richard

Stallman in 1984 and may well be called GNU/Linux.



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Command Interpreter

There are other system softwares (utilities) thatare essential for the use of a computer system.One most visible and important software is thecommand interpreter e.g. bash. We shall talkmore about it afterward.



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Our C Programming Environment

• PC with Intel Pentium IV CPU(+ MMU +

cache).

• Operating System, Linux (redhat).

• Command interpreter, bash (Bourne-again

shell).

• Editor, emacs or vi.



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Our C Programming Environment

• Compiler, GNU gcc for C languagea.

• Assembler, as.

• Linker (link-editor), ld.

agcc is actually a C++ compiler.



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Our OCAML Programming Environment

• OCAML (Objective Caml) is a language

designed by INRIA (Institut National de

Recherche en Informatique et Automatique),

France.

• Interpreter, OCAML or CAML Light.

• Editor, emacs or vi.



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First C Program

#include <stdio.h>

int main()

{

printf("The First C Program\n");

return 0;

} // first.c



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Write, Compile and Execute on Linux OS

1. Use an editor e.g. ‘vi’ or ‘emacs’.

• Run (execute) the editor program.

• Key-in the C program text.

• Save the program as a named file e.g.

‘first.c’.

2. Compile the C program to the executable file

‘a.out’.



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3. If there is an error, go back to the editor and

fix it; otherwise run the ‘a.out’ file and get

the output.



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Typical Commands Are

• $ emacs first.c &

• $ cc -Wall first.c

• $ ./a.out

My first program



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Note

• The compiler creates the executable filea

‘a.out’ (assembler output) from the C

program file ‘first.c’.

aIt contains the machine code and some other data.



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OCAML Interpreter

$ ocaml

Objective Caml version 3.10.1

# #quit;;$



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First OCAML Program

$ ocaml


#print_string("My first OCAML program\n");;My first OCAML program- : unit = ()#



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Example - II

Write a C program that reads a positive integer

n and finds the sum 0 + 1 + · · ·+ n = n(n+1)2 .



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#include <stdio.h>

int main()

{

int n;

printf("Enter a +ve integer: ");

scanf("%d", &n);

if(n < 0)

printf("Incorrect data: %d\n", n);

else printf("0+ ... +%d = %d\n",n,n*(n+1)/2);

return 0;

} // second.c



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Example - IIa

Write an OCAML program that takes n as aparameter and computes the sum

0 + 1 + · · ·+ n = n(n+1)2 .



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$ ocaml


# let sumN = function n -> n*(n+1)/2;;

val sumN : int -> int = <fun>

# sumN 10;;

- : int = 55

# sumN (-10);;

- : int = 45

#



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Laboratory Session



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Let’s Start At The Very Beginning

• How to Start a Computer?

• How to write a C and OCAML Program?

• How to Compile a C Program to an

Executable Module?

• How to Run (Create a Process with) an

executable Module?



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How to Start & Stop the Machine



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1. Power On the machine (main cabinet and

VDU).

2. Select the Linux option.

3. Enter the login name and then the password.

The login name is user and the password is

user123.

4. Open one or two windows on the VDU (use

the icon).



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1. One window is active at a time - use the

mouse to activate an window.

2. A window may be closed by pressing Ctrl-D.



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Power-off the Machine

1. Close all windows.

2. logout from the machine (use the icon).

3. Shutdown the system.

4. Power-off the VDU (power of the main

cabinet will be put-off automatically).



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How to Start the Emacs Editor

• Select an window and enter the command

emacs & .

• An emacs window is created.

• You may select the font size.

• Close the emacs window selecting the Exit

emacs entry of the File menu.



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Write, Compile and Execute a C Program

1. Start the emacs editor: emacs &

2. Select Open File of the File menu.

3. Give a file name: first.c (at the bottom of

the emacs window).

4. Type the following C Program and finally

save the buffer as a file first.c : Save Buffer

of File menu.



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Starting OCAML Interpreter

1. $ ocaml

2. The interpreter comes up with the following

prompt:


#



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Activity - I

Enter the first program (first.c), compile andexecute.Enter the corresponding OCAML program inthe interpreter.



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If There is an Error

#include <stdio.h>

int main()

// Syntax error

printf("The First C Program\n");

return 0;

} // first.c



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Compiler Message

$ cc -Wall first.cfirst.c:4: error: syntax error before"printf"first.c:4: warning: type defaults to‘int’ .... ‘printf’first.c:4: error: conflicting typesfor ’printf’.............



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What to do?

1. Open the file first.c in emacs.

2. Identify and fix the errors.

3. Save the modified file (same name).

4. Compile it again.

Any time you make a change in the file, save itand compile it to get the new executablemodule, a.out.



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Note

1. If there is no more message from the

compiler, the C program is syntactically

correct (well-formed).

2. An well-formed C program may have logical

error. Error-free compilation does not

guarantee the logical correctness of a

program.



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OCAML Error Message

# print strng("First OCAML program\n");;Unbound value print_strng#Incorrect function name.



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OCAML Error Message

#print_string("First OCAML program\n";;Syntax error: ’)’ expected,the highlighted ’(’ might be unmatched#



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Note

An OCAML program can be written in a filewith the file name extension .ml. The file canbe given to the interpreter for interpretation.Let the file name be first.ml with the content

(* First program *)print_string("First OCAML program\n");;



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OCAML Program from a File

$ ocamlObjective Caml version 3.10.1

# #use "first.ml";;First OCAML program- : unit = ()#



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Activity - II

• Enter the second program (second.c),

compile and execute. Write the

corresponding OCAML function sumN

• Modify the second program to compute

12 + 22 + 32 + · · ·+ n2 = n(n+1)(2n+1)6 . Write

the corresponding OCAML function sumNsq.



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Activity - II

File second.ml(* Sum of n natural numbers *)let sumN = function n -> n*(n+1)/2;;



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Integer Operators

C OCAML

+ - * / + - * /

% mod

abs() abs

abs() in C is not an operator but a libraryfunction. Its prototype is defined in stdlib.h.



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Example - III

A program in C that reads a positive number ras the radius of a circle and computes its areausing the formula A = πr2 is as follows.The corresponding OCAML function iscircArea.



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#include <stdio.h>

#include <math.h>

int main() {

double radius, area ;

printf("Enter the radius: ");

scanf("%lf", &radius) ;

area = M_PI*radius*radius ;

printf("Circle-Area = %lf for Radius = %lf\n",

area, radius);

return 0 ;

} // Area of a circle third.c



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OCAML Program third.ml

(* Area of a circle *)let circArea rad = 3.14159 *. rad *. rad;;

(* third.ml *)let cArea r =

print_string("Radius: ");print_float(r);print_string(" => Area: ");print_float(circArea r);print_newline();;



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Note

The floating-point operator ‘*.’ is differentfrom the integer operator ‘*’ - otherflaoting-point operators are ‘+.’ ‘-.’ ‘/.’



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Activity - III

• Enter the C program, compile and execute.

Enter the OCAML function.

• Modify the program to compute the

perimeter of a circle using the formula

C = 2πr. Write the corresponding OCAML

function circPeri.



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Example - IV

We write a C program that reads a temperaturein degree Fahrenheit and converts it to theequivalent temperature in degree Celsius. Weknow that 32◦F ≡ 0◦C and 212◦− 32◦ = 180◦ ofFahrenheit scale is equivalent to100◦ − 0◦ = 100◦ of Celsius scale. So atemperature F in the Fahrenheit scale is relatedto the equivalent temperature C in the Celsiusscale as F−32

180 = C−0100−0 i.e. C = 5

9(F − 32)



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#include <stdio.h>

int main(){

float cel, fah;

printf("Enter temp. in F: ");

scanf("%f", &fah);

cel = 5.0*(fah-32.0)/9.0 ;

printf("%6.2f F = %6.2f C\n", fah, cel);

return 0;

} // Fahrenheit to Celsius: fourth.c



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OCAML Function and Programs

let fToc f=5.0*.(f-.(float)32)/.9.0;;

(* fourth.ml *)

let fahToCel fah =

print_float(fah);

print_string(" F = ");

print_float(fToc fah);

print_string(" C\n");;



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Activity - IV


Enter the OCAML program in interpreter.

• Modify the program to read a temperature in

Celsius scale and convert it to the equivalent

temperature in the Fahrenheit scale.



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Getting the Slides

• Run Mozilla and access

http://facweb.iitkgp.ernet.in/∼goutam

• Follow the link

Summer School for the School Students

... of Summer: 2009.

• Download the correct .ps/.pdf file.



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Display the Slides

• View the slides using either kghostview or

ggv.

• $ kghostview lect1.ps &a

• Select the View → Orientation to Seascape

for proper view.

aOr, $ ggv lect1.ps &. You must use ‘&’. Use xpdf or acroread for .pdf file.



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Example - V

Write a C program to read two integers andprint the larger one.



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#include <stdio.h>

int main() {

int first, second, max ;

printf("Enter two integers :") ;

scanf("%d%d", &first, &second) ;

if(first > second) max = first ;

else max = second ;

printf("\nMax(%d,%d) = %d\n",

first, second, max) ;

return 0 ;

} // Larger fifth.c



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Two OCAML Programs

let larger a b = if a > b then a else b ;;

let lrgr a b = (* fifth.ml *)

if a > b then

begin

print_int(a); print_string(" > ");

print_int(b); print_newline()

end

else

begin

print_int(a); print_string(" <= ");

print_int(b); print_newline()

end;;



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Activity - V


Same for OCAML program.

• Modify the program to print the smaller one.

• Modify the program to read three integers

and print the largest one.



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Example - VI

Following C program reads a two-digit positiveinteger say mn and converts it to the form nm.Same is the effect of the OCAML program.



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#include <stdio.h>

int main()

{

int n ;

printf("Enter a two-digit integer: ");

scanf("%d", &n);

if(n < 10 || n >= 100) printf("Wrong data: %d\n", n);

else printf("%d --> %d\n", n, 10*(n%10)+n/10);

return 0;

} // mn --> nm ex6.c



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OCAML Function

exception OutOfRange;;

let revDig x =

if x < 10 || x >= 100 then raise OutOfRange

else 10*(x mod 10)+x/10;;



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OCAML Program

let revD x = (* ex6.ml *)

if x < 10 || x >= 100 then raise OutOfRange;

print_string("Reverse(");

print_int(x);

print_string(") = ");

print_int(revDig x);

print_newline();;



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Activity - VI

• Enter the program, compile and execute.

• Modify the program to print the sum of two

digits.

• Modify the program to print the arithmetic

mean of the two digits, m+n

2 .



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Example - VII

Following C program reads a positive integer nand then reads n numbers a1, a2, · · · , an andprints the largest among them. Same for theOCAML program.



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#include <stdio.h>

int main()

{

int n, i;

float data, max;

printf("Enter a positive integer: ");

scanf("%d", &n);

if(n < 1) {

printf("Wrong count: %d\n",n);

return 0;

}

printf("Enter %d data:\n",n);

scanf("%f", &max);



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for(i=2; i<=n; ++i){

scanf("%f", &data);

if(max < data) max = data;

}

printf("The largest data is: %f\n", max);

return 0;

} // largest among n data ex7.c



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OCAML Program

(* Largest among n data. One data per line *)

exception DataCountError

let maxDat() =

print_string("Enter Data Count\n");

let n = read_int() in

if n < 1 then raise DataCountError

else

begin

print_string("Enter data:\n");

let max = ref (read_int()) in

begin

for i=2 to n do



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let data = read_int() in

if !max < data then max := data;

done;

print_string("Largest data: ");

print_int(!max);

print_newline();

end

end;; (*ex7.ml*)



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Activity - VII

• Enter the program, compile and execute.

• Modify the program to print the smallest

among n data.

• Modify the program to print the arithmetic

mean of n data AM = a1+a2+···+an

n.

• Modify the program to find the second

largest among n(≥ 1) data.


summer school - facweb.iitkgp.ac.ingoutam/sss/lect/lect1.pdf · machine language program a nite...

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