lec 8 lang hardware_001

7/30/2019 Lec 8 Lang Hardware_001

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Computer Languages

Machine Language A collection of binary numbers Not standardized. There is a different machine language for

every processor family.

Assembly Language- mnemonic codes that corresponds

to machine language instructions. Low level: Very close to the actual machine language.

High-level Languages- Combine algebraic expressionsand symbols from English High Level : Very far away from the actual machine language

For example: Fortran, Cobol, C, Prolog, Pascal, C#, Perl, Java.

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Example of ComputerLanguages

char name[40];printf("Please enter your name\n");scanf("%s", name);printf("Hello %s", name);

push offset string "Please enter your name\n"(41364Ch)call dword ptr [__imp__printf (415194h)]

add esp,4lea eax,[name]push eaxpush offset string "%s" (413648h)call dword ptr [__imp__scanf (41519Ch)]add esp,8lea eax,[name]push eaxpush offset string "Hello %s" (41363Ch)

call dword ptr [__imp__printf (415194h)]add esp,8

68 4C 36 41 00 FF 15 94 51 41 00 83 C4 04 8D 45 D850 68 48 36 41 00 FF 15 9C 51 41 00 83 C4 08 8D 45D8 50 68 3C 36 41 00 FF 15 94 51 41 00 83 C4 08

C Source Code:

Assembly Code:

Machine Code:

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Compiler

Compilation is the process of translating the source code(high-level) into executable code (machine level).

Source file - A file containing the program code

A Compiler turns the Source File into an Object File

Object file - a file containing machine languageinstructions

A Linker turns the Object File into an Executable

Integrated Development Environment (IDE) - a program

that combines simple word processing with a compiler,linker, loader, and often other development tools

For example, Eclipse or Visual Studio

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C Programming

An introduction


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History The initial development of C occurred at

AT&TBell Labs between 1969 and 1973. It is developed in 1972 by Dennis Ritchie

The origin of C is closely tied to the

development of the Unix operating system, It was named "C" because many of itsfeatures were derived from an earlierlanguage called "B", which according to

Ken Thompson was a stripped-downversion of the BCPL (Basic CombinedProgramming Language).

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http://en.wikipedia.org/wiki/AT&Thttp://en.wikipedia.org/wiki/Bell_Labshttp://en.wikipedia.org/wiki/Dennis_Ritchiehttp://en.wikipedia.org/wiki/Unixhttp://en.wikipedia.org/wiki/B_(programming_language)http://en.wikipedia.org/wiki/Ken_Thompson_(computer_programmer)http://en.wikipedia.org/wiki/BCPLhttp://en.wikipedia.org/wiki/BCPLhttp://en.wikipedia.org/wiki/Ken_Thompson_(computer_programmer)http://en.wikipedia.org/wiki/B_(programming_language)http://en.wikipedia.org/wiki/Unixhttp://en.wikipedia.org/wiki/Dennis_Ritchiehttp://en.wikipedia.org/wiki/Bell_Labshttp://en.wikipedia.org/wiki/AT&T


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Programming

Programming - scheduling, or performing a task or anevent.

Computer Programming - creating a sequence of stepsfor a computer to follow in performing a task.

Programming Language - a set of rules, symbols, andspecial words used to construct a computer program.

Programming language rules consist of:

Rules of Syntax which specify how valid instructions are writtenin the language.

Rules of Semantics which determine the meaning of theinstructions (what the computer will do).

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A SIMPLE C PROGRAM

The following program is written in the Cprogramming language.

#include

main()

{

printf ("Programming in C is easy.\n");

}Sample Program Output:Programming in C is easy.

_

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A NOTE ABOUT C PROGRAMS

In C, lowercase and uppercase charactersare very important! All commands in C mustbe in lowercase.

The C programs starting point is identified

by the word main() This informs the computer as to where the

program actually starts.

The brackets that follow the keyword mainindicate that there are no argumentssupplied to this program (this will beexamined later on).

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Contd

The two braces, { and }, signify the beginand end segments of the program.

The purpose of the statment :

#include is to allow the use of the printfstatementto provide program output.

Text to be displayed byprintf() must be

enclosed in double quotes . The program has only one statement

printf("Programming in C is easy.\n")9
http://gd.tuwien.ac.at/languages/c/programming-bbrown/c_011.htmhttp://gd.tuwien.ac.at/languages/c/programming-bbrown/c_011.htm


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printf() is actually a function in C that is

used for printing variables and text. Wheretext appears in double quotes "", it isprinted without modification.

There are some exceptions however. Thishas to do with the\ and % characters.These characters are modifier's, and for

the present the\ followed by the ncharacter represents a newline character.

Contd

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Another important thing toremember is that all C

statements are terminatedby a semi-colon ;

Contd

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Summary of major points

program execution begins at main() keywords are written in lower-case statements are terminated with a semi-colon text strings are enclosed in double quotes

C is case sensitive, use lower-case and try notto capitalise variable names \nmeans position the cursor on the beginning of

the next line

printf() can be used to display text to the screen the curly braces { } define the beginning andend of a program block

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CLASS EXERCISE1

Q1.1. What is the output of following program ?

#include

main(){

printf("Programming in C is easy.\n");

printf("And so is Pascal.\n");

}

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ANSWER 1.1

Programming in C is easy.And so is Pascal.

_

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Process of Program execution

The diagram of program execution is given on next

Page:----

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Fig 1.12Entering,Translating,and Runninga High-LevelLanguageProgram

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Q1.2 What is the output of following program ?

#include

main()

{

printf("The black dog was big. ");

printf("The cow jumped over the moon.\n");

}

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ANSWER 1.2

The black dog was big. The cow jumped over the moon.

_

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Q1.3Try and work out what the following

program displays,

#include

main(){

printf("Hello...\n..oh my\n...when do i stop?\n");

}

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ANSWER 1.3

Hello...

..oh my

...when do i stop?

_

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KEYWORDS Keywords are words reserved by C so

they cannot be used as variables.Keywords

auto double int struct

break else long switch

case enum register typedef

char extern return union

const float short unsigned

continue for signed void

default goto sizeof volatile

do if static while


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Variables & Data Types

Declaring a variable reserves enoughbytes in memory to store value of thedeclared type.

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Contd

C provides the programmer with FOURbasic data types

These are:

integercharacter

float

double

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Contd

The basic format for declaring variables is

data_type var, var, ... ;

where data_type is one of the four basictypes, an integer, character, float, ordouble type.

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DATA TYPE DESCRIPTION MEMORYREQUIRMENT

int Integer quantity 2 bytes(-32767 ,32767)

Long int Integer quantity 4 bytes

float A number containing adecimal point

4 bytes

(1E-37 to 1E+37)

char Any character 1 byte (-127 to 127)

double A number containing adecimal point but here wecan have more significantfigures.

8 bytes

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Contd User defined variables must be declared

before they can be used in a program.

Get into the habit of declaring variablesusing lowercase characters. Remember

that C is case sensitive, so even though thetwo variables listed below have the samename, they are considered different

variables in C. sum

Sum

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Contd

The declaration of variables is done after theopening brace ofmain(),

e.g.

#include

main(){

int sum;

sum = 500 + 15;printf("The sum of 500 and 15 is %d\n", sum);

}

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General Form of printf() function

printf(,);

can contain

%d for printing integer values.

%f for printing real values.%c for printing character values.

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scanf() function

scanf(format specifier,& list of vaiables)

Again format specifier is same as in case of printf().

And & is address of operator.

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Some of the formatters forprintfare

1. Cursor Control Formatters

\n new line

\t tab

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Contd

2. Variable Formatters%d decimal integer

%c character

%s string or character array

%f float

%e double

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CLASS EXERCISE2

Q2.1 What is the output of the following program?

#include

main()

{int value1, value2, sum;

value1 = 35;

value2 = 18;

sum = value1 + value2;

printf("The sum of %d and %d is %d\n", value1, value2, sum);

}

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ANSWER2.1

The sum of 35 and 18 is 53_

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MORE ABOUT VARIABLES

Variables must begin with a character orunderscore, and may be followed by anycombination of characters, underscores, or thedigits 0 - 9.

The following is a list of valid variable names:summaryexit_flagI

Jerry7Number_of_moves

_valid_flag

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Contd You should ensure that you use

meaningful names for your variables. Thereasons for this are:

meaningful names for variables are self

documenting (see what they do at aglance)

they are easier to understand

there is no correlation with the amount ofspace used in the .EXE file

makes programs easier to read

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CLASS EXERCISE 3

Q3.1 Why are the variables in thefollowing list invalid,

value$sum

exit flag

3lotsofmoney char

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ANSWER3.1

value$sum contains a $

exit flag contains a space 3lotsofmoney begins with a digit

char is a reserved keyword

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COMMENTS

The addition of comments inside programsis desirable.

These may be added to C programs byenclosing them as follows:

/* bla bla bla bla bla bla */

Note that the/* opens the comment fieldand */ closes the comment field.Comments may span multiple lines.

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Contd

Comments may not be nested one insideanother. For e.g.

/* this is a comment. /* this comment isinside */ wrong */

In the above example, the first occurrenceof*/ closes the comment statement for theentire line, meaning that the text wrongisinterpreted as a C statement or variable,and in this example, generates an error.

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What Comments Are Used For

Documentation of variables and theirusage

Explaining difficult sections of code Describes the program, author, date,

modification changes, revisions etc

Copyrighting

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PREPROCESSOR


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PREPROCESSORSTATEMENTS

Note that preprocessor statements beginwith a # symbol, and are NOT terminatedby a semi-colon.

Preprocessor statements are handled bythe compiler (or preprocessor) before theprogram is actually compiled.

In general, preprocessor constants arewritten in UPPERCASE

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Contd

The define statement is used to makeprograms more readable.

Consider the following examples:

#define TRUE 1#define FALSE 0

#define NULL 0

#define AND &

#define OR |

#define EQUALS ==

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HEADER FILES

Header files contain definitions offunctions and variables which can beincorporated into any C program by using

the pre-processor#include statement. Standard header files are provided with

each compiler, and cover a range ofareas, string handling, mathematical, dataconversion, printing and reading ofvariables.

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Contd

To use any of the standard functions, theappropriate header file should be included.

This is done at the beginning of the C

source file. For example, to use thefunctionprintf() in a program, the line

#include

should be at the beginning of the sourcefile, because the definition forprintf() isfound in the file stdio.h

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Contd

All header files have the extension .h andgenerally reside in the/include subdirectory.

The use of angle brackets informs thecompiler to search the compilers include

directory for the specified file. The use of the double quotes " around the

filename inform the compiler to search in thecurrent directory for the specified file.

#include "mydec.h"

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The only characters required by the C ProgrammingLanguage are as follows:

A - Za -z0 - 9

space . , : ; ' $ "# % & ! _ {} [] () < > |

+ - / * =

C character set

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V i bl C t t d


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Variables, Constants andKeywords

Variables:-It is a name given to a memorylocation to store a value of a data that aprogram is working on.

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R l f t ti V i bl


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Rules for constructing Variablenames

(1) A variable name is any combination of 1to 31 alphabets, digits or underscores butthere is some restriction on the length of

variables that depends on compiler tocompiles. Do not create unnecessarilylong variable names as it adds to youreffort.

(2) The first character in the variable namemust be an alphabet or underscore.

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Continued

(3) No commas or blanks are allowed withina variable name.

(4) No special symbol other than an

underscore can be used in a variablename.

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Keywords:

Keywords are words reserved by C sothey cannot be used as variables.

Keywords

auto double int structbreak else long switch

case enum register typedef

char extern return union

const float short unsigned

continue for signed void

default goto sizeof volatile

do if static while

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Data Types.

Type of value that a variable can hold iscalled data type of a variable.

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continued


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continuedDATA TYPE DESCRIPTION MEMORY

REQUIRMENT

int Integer quantity 2 bytes(-3276732767)

Long int Integer quantity 4 bytes

float A number containing adecimal point

4 bytes

(1E-37 to1E+37)

char Any character 1 byte (-127 to 127)

double A number containing adecimal point but herewe can have moresignificant figures.

8 bytes

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Declaringvariable

In order to use a variable in a C program, youmust first declare it.

You declare a variable with a declaration.

int x=5; As in the example shown above, a declaration of

a variable consists of the variables type followed

by the variables name and then a semicolon.

There must be whitespace between the type andthe name.

It is also possible to declare multiple variables

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Constants

A constant is an entity that doest change

its value while a variable is an entity thatmay change.

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Types of C constants

(a) Primary constants. i.e. integer, real andcharacter constants.

(b) Secondary constants. i.e. Array, pointer,

structure, union and enum etc.

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