chapter1 introduction new

7/29/2019 Chapter1 Introduction New

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Principles of Programming - NI July 2005 1

Chapter 1: Introduction

In this chapter you will learn about:Overview of PC components

The different types of language

Natural Language

Formal Language

Functional / Imperative Language

Programming Languages

C as an imperative language

C program at a glance


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Computer Hardware Components

Components of a PC


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Input / Output Devices

Input DevicesAccepts information from the user and transformsit to digi ta l codesthat the computer can process

Example: keyboard, mouse, scanner

Output DevicesAn interfaceby which the computer conveys theoutput to the user

Example: monitor, printer


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Main Memory

A semiconductor device which stores theinformation necessary for a program to run.2 types

ROM (Read Only Memory)

Contains information that is necessary for the

computer to boot upThe information stays there permanently even whenthe computer is turned off.

RAM (Random Access Memory)

Contains instruction or data needed for a program torun

Got erased when the computer is turned off.


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Central Processing Unit (CPU)

Does most of the work in executing a programThe CPU inside a PC is usually the microprocessor

3 main parts:Control Unit

Fetch instructions from main memory and put them inthe instruction register

ALU (Arithmetic Logic Unit)Execute arithmetic operations

Registers

Temporarily store instructions or data fetched frommemory


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Storage Devices

A magnetic device used to store a large amountof information.

Store the software components or data neededfor the computer to execute its tasks.

Could be read only or writable.

Example: Hard drive, CD ROM, floppy disks


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Network Devices

Connect a computer to the other computers.Enable the users to access data or executeprograms remotely.

Example: modem, Ethernet card


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Natural language

Our everyday-language; spoken and writtenNot 100% needed to understand:

Do you want to buy this computer ? remainscomprehensible

Depends on circumstances; the context:

Do you like one ? doesn't make sense on its own.It needs a situation around it: someone holding a bouquet of flowers: you might

take one

someone pointing to an expensive car: your opinionis asked

someone 'offers' you an oily cloth to sneeze: youdon't take it


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Semantics and Syntax

Semantics the meaning of the language within agiven context

Syntax - Syntax are the rules to join words

together in forming a correct expressionor

phrase.In natural languages it is often possible toassemble a sentence in more than one correctways.


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Formal Language

Language with limited, defined, wordsEach concatenation of words ('phrase') has asingle, clearly defined meaning

no (miss-)interpretation possible

Sometimes called Context Free Language

To 'talk' to a computer; to instruct a computer; ourcommands must be 100% clear and correct.

Often there is only a single, correct syntax.


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Functional / Imperative Language

Functional Language:Tell what to do, but not how:

sum [1...10]

Imperative Language:Tell what to do, but mainly how:

Take number 1 and add the next number to it;

then add the next number to the sum; and so on;

until you have reached 10 as number to be added.Then print the sum of all numbers


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What is Programming?

Programmingis instructing a computer to do somethingfor you with the help of a programming language

The two roles of a programming language:

Technical: It instructs the computer to perform tasks.

Conceptual: It is a framework within which we

organize our ideas about things and processes.In programming, we deal with two kind of things:

Data - representing 'objects' we want to manipulate

Procedures-'descriptions' or 'rules' that define howtomanipulate data.


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Programming Language

Formal Language used to communicate to acomputer.

A programming language contains inst ruct ionsfor the computer to perform a specific action or a

specific task:'Calculate the sum of the numbers from 1 to 10

'Print I like programming

'Output the current time'


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Programming Language

Can be classified into as a special-purpose andgeneral-purpose programming languages.

Special-purpose : is design for a particular type ofapplication

Structured Query Language (SQL)

General-purpose : can be used to obtain solutionsfor many types of problems

Machine Languages

Assembly Languages

High-Level Languages


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Machine Language

The only language that the processor actually'understands

Consists of binary codes: 0 and 1Example: 00010101

11010001

01001100Each of the lines above corresponds to a specific taskto be done by the processor.

Programming in machine code is difficult and slowsince it is difficult to memorize all the instructions.

Mistakes can happen very easily.Processor and Architecture dependent


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Assembly Language

Enables machine code to be representedin words andnumbers.

Example of a program in assembler language:

LOAD A, 9999

LOAD B, 8282

SUB B

MOV C, ALOAD C, #0002

DIV A, C

STORE A, 7002

Easier to understand and memorize (called Mnemonics),

compared to machine code but still quite difficult to use.Processor and Architecture dependent


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High-Level Language

Use more English words. They try to resemble Englishsentences. Therefore, it is easier to program in theselanguages.

The programming structure is problem oriented - does notneed to know how the computer actually executestheinstructions.

Processorindependent - the same code can be run ondifferent processors.

Examples: Basic , Fort ran , Pascal, Cobol , C, C++, Java

A high level language needs to be analyzed by the compiler

and then compiled into machine code so that it can beexecuted by the processor.


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C Programming Language

Why 'C' ?Because based on 'B'; developed at Bell Laboratories

Developed by Dennis Ritchie at Bell Laboratories inthe 1960s

In cooperation with Ken Thomson it was used forUnix systems

The C Language was only vaguely defined, notstandardized, so that almost everyone had his ownperception of it, to such an extend that an urgent

need for a standard code was creeping up


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C Programming Language cont

In 1983, the American National Standards Institute(ANSI) set up X3J11, a Technical Committee to drafta proposal for the ANSI standard, which wasapproved in 1989 and referred to as the ANSI/ISO9899 : 1990 or simply the ANSI C, which is now theglobal standard forC.

This standard was updated in 1999; but there is nocompiler yet


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C An Imperative Language

C is a highly imperative languageWe must tell it exactly how to do what;

the means and functions to use;

which l ibrariesto use;

when to add a new line;when an instruction is finished;

in short: everything and anything

Hint: Observe thesyntax

in the next slide


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A Simple Program in C

#include

main()

{ printf("I like programming in C.\n");

}


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A Simple Program in C - explanation

#include

main(){

printf("I like programming in C.\n");

}

standard Library, input-output, header-file

Begin of program

End of statement

End of Segment

Start of Segment

Function for printing text

Insert a new line


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C Output

I like programming in C.


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Summary

We have looked at some underlying hardwareWe have seen some different types of languages;

the relevance ofsemantics and syntax.

We have observed the detail necessary in animperative language to instruct a computerproperly.

Finally, we examined the syntax to print a line oftext to the screen of our computer.

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