Introduction

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Principles of Programming - NI July 20 05 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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Transcript of Introduction

Page 1: Introduction

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 languageNatural 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 transforms it to digital codes that the computer can processExample: keyboard, mouse, scanner

Output DevicesAn interface by which the computer conveys the output to the userExample: monitor, printer

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Main Memory

A semiconductor device which stores the information 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 when the computer is turned off.

RAM (Random Access Memory)Contains instruction or data needed for a program to runGot 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 microprocessor3 main parts:

Control UnitFetch instructions from main memory and put them in the instruction register

ALU (Arithmetic Logic Unit)Execute arithmetic operations

RegistersTemporarily store instructions or data fetched from memory

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Storage Devices

A magnetic device used to store a large amount of information.Store the software components or data needed for 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 execute programs 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 ?” remains comprehensible

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 opinion is asked

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

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Semantics and Syntax

Semantics – the meaning of the language within a given context

Syntax - Syntax are the rules to join wordstogether in forming a correct expression or phrase.

In natural languages it is often possible to assemble a sentence in more than one correct ways.

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Formal Language

Language with limited, defined, words

Each concatenation of words ('phrase') has a single, clearly defined meaning

no (miss-)interpretation possible

Sometimes called “Context Free Language”

To 'talk' to a computer; to instruct a computer; our commands 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?

Programming is instructing a computer to do something for you with the help of a programming languageThe 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 manipulateProcedures -'descriptions' or 'rules' that define how to manipulate data.

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Programming Language

Formal Language used to communicate to a computer.

A programming language contains instructions for 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 and general-purpose programming languages.Special-purpose : is design for a particular type of application

Structured Query Language (SQL)General-purpose : can be used to obtain solutions for 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 1

Example: 00010101 11010001 01001100

Each of the lines above corresponds to a specific task to be done by the processor.Programming in machine code is difficult and slow since 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 represented in words and numbers.Example of a program in assembler language:

LOAD A, 9999LOAD B, 8282SUB BMOV C, ALOAD C, #0002DIV A, CSTORE 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 LanguageUse more English words. They try to resemble English sentences. Therefore, it is easier to program in these languages.

The programming structure is problem oriented - does not need to know how the computer actually executes the instructions.

Processor independent - the same code can be run on different processors.

Examples: Basic, Fortran, 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 be executed 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 in the 1960s

In cooperation with Ken Thomson it was used for Unix systems

The C Language was only vaguely defined, not standardized, so that almost everyone had his own perception 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 draft a proposal for the ANSI standard, which was approved in 1989 and referred to as the ANSI/ISO 9899 : 1990 or simply the ANSI C, which is now the global standard for C.

This standard was updated in 1999; but there is no compiler yet

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C – An Imperative Language

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

the means and functions to use;

which libraries to use;

when to add a new line;

when an instruction is finished;

in short: everything and anything…

Hint: Observe the syntax in the next slide

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A Simple Program in C

#include <stdio.h>

main(){

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

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A Simple Program in C - explanation

#include <stdio.h>

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 hardware

We have seen some different types of languages;the relevance of semantics and syntax.

We have observed the detail necessary in an imperative language to instruct a computer properly.

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


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