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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.