Lecture1 Introduction To Computers And Programming Language

BITG 1113: Introduction To Computers And Programming Language

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Objectives In this chapter, you will: • Learn about different types of computers • Explore the hardware and software components of a computer system • Learn about the language of a computer • Learn about the evolution of programming languages • Examine high-level programming languages LECTURE 1

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Objectives (cont.) • • • •

Discover what a compiler is and what it does Examine a C++ program Explore how a C++ program is processed Become aware of Standard C++ and ANSI/ISO Standard C++

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Why Program? • Computer – programmable machine designed to follow instructions • Program – instructions in computer memory to make it do something • Programmer – person who writes instructions (programs) to make computer perform a task • SO, without programmers, no programs; without programs, a computer cannot do anything LECTURE 1

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Categories of Computers • Mainframe computers • Midsize computers • Micro computers (personal computers)

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Computer Components Computer is an electronic device, with two major components. Computer Hardware

Software

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Main Hardware Component Categories: 1. 2. 3. 4. 5.

Central Processing Unit (CPU) Main Memory Secondary Memory / Storage Input Devices Output Devices

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Main Hardware Component Categories

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Central Processing Unit (CPU) Comprised of: – Control Unit • Retrieves and decodes program instructions • Coordinates activities of all other parts of computer

– Arithmetic & Logic Unit • Hardware optimized for high-speed numeric calculation • Hardware designed for true/false, yes/no decisions

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CPU Organization

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Main Memory • It is volatile. Main memory is erased when program terminates or computer is turned off • Also called Random Access Memory (RAM) • Organized as follows: – bit: smallest piece of memory. Has values 0 (off, false) or 1 (on, true) – byte: 8 consecutive bits. Bytes have addresses.

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Main Memory • Addresses – Each byte in memory is identified by a unique number known as an address.

The number 149 is stored in the byte with the address 16, and the number 72 is stored at address 23. LECTURE 1

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Main Memory

Main memory with some data

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Secondary Storage • Non-volatile: data retained when program is not running or computer is turned off • Comes in a variety of media: – magnetic: floppy disk, zip disk, hard drive – optical: CD-ROM – Flash drives, connected to the USB port

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Input Devices • Devices that send information to the computer from outside • Many devices can provide input: – Keyboard, mouse, scanner, digital camera, microphone – Disk drives and CD-ROM (Secondary storage)

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Output Devices • Output is information sent from a computer program to the outside world. • The output is sent to an output device • Many devices can be used for output: – Computer monitor and printer – Floppy, zip disk drives, writable CD drives (Secondary storage)

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Computer Software •Software: programs that do specific tasks. • Software is divided into 2 categories Software

System Software

Application Software

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System Software • Related software that manages the system’s resources and control the operations of the hardware. • Normally supplied by the manufacturer of the computer. • Consists of utility programs and operating aids that facilitate the use and performance of the computer. • System programs take control of the computer, such as an operating system. • Operating system are programs that manage the computer hardware and the programs that run on them. Examples: Windows, UNIX, Linux. LECTURE 1

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Application Software • Programs that provide services to the user. • Designed to perform a specific task (such as course registration or banking) OR a generalpurpose task (such as word processing, eg. Ms Word). • May be acquired by purchasing off-the-shelf or by designing for own purpose (custome made). • Off-the-shelf : prewritten and ready to use. • Custom made : written by in-house, consulting firm or software house. LECTURE 1

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Where are the application and system software?

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Computing Environment Personal Computing Time-Sharing Client / Server Computing Internet Computing LECTURE 1

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Personal computing environment Picture 2

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Time-sharing environment

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The client/server environment Picture 2

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The Language of a Computer • Digital signals are sequences of 0s and 1s • Machine language: language of a computer • Binary digit (bit): – The digit 0 or 1

• Binary code: – A sequence of 0s and 1s

• Byte: – A sequence of eight bits LECTURE 1

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Coding Schemes • ASCII (American Standard Code for Information Interchange) – 128 characters – A is encoded as 1000001 (66th character) – 3 is encoded as 0110011

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Coding Schemes (cont.) • EBCDIC – Used by IBM – 256 characters

• Unicode – 65536 characters – Two bytes are needed to store a character

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History Of Computer Languages

Computer language evolution The only language understood by a computer is machine language LECTURE 1

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History Of Computer Languages (cont.) 1.Machine Language • Computer only understand this language. • Series of 1’s and 0’s (binary numbers), such as 1011010000000101 • Difficult to write. • Low level language

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History Of Computer Languages (cont.) • Early computers were programmed in machine language • To calculate wages = rates * hours in machine language: 100100 010001 100110 010010 100010 010011

//Load //Multiply //Store

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History Of Computer Languages (cont.) 2. Symbolic/Assembly Language • Unique to particular computer. • Use mnemonics symbols. E.g. “MUL” –Multiply • Easier to understand.

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History Of Computer Languages (cont.) • Using assembly language instructions, wages = rates • hours can be written as: LOAD rate MULT hour STOR wages

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History Of Computer Languages (cont.) 3. High-Level Language • Portable to many different computers. • Instruction are coded • Eg. COBOL (Business), FORTRAN (Scientific), BASIC, Pascal, C, C++, C#, Java etc. • Programmers use this to write programs. • Compiler: translates a program written in a high-level language machine language • The equation wages = rate x hours can be written in C++ as: wages = rate * hours; LECTURE 1

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History Of Computer Languages (cont.) 4. Natural Language • Like our natural language (such as English, French, or Chinese) • Its use is still quite limited.

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Programs and Programming Languages • Types of languages: – High-level: closer to human language

– Low-level: used for communication with computer hardware directly. Often written in binary machine code (0’s/1’s) directly. LECTURE 1

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Some Well-Known High-Level Programming Languages

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Example of a C++ Program #include using namespace std; int main() { cout << "My first C++ program." << endl; cout << "The sum of 2 and 3 = " << 5 << endl; cout << "7 + 8 = " << 7 + 8 << endl; return 0; } Sample Run: My first C++ program. The sum of 2 and 3 = 5 7 + 8 = 15

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Program Development • A computer understands a program only if the program is coded in its machine language. • Programmer have to write the program and turn it into an executable (machine language) code. • Programmer have to understand the problem -> break into actions-> execute by the computer. LECTURE 1

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From a High-level Program to an Executable Code • • • •

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There are 4 steps in the process : Create and edit file containing the program with a text editor. Run preprocessor to process the preprocessor directives (begin with #) Run compiler to: • Check that the program obeys the rules • Translate into machine language (object code) Run linker to connect hardware-specific code to machine instructions, producing an executable code. Steps b–d are often performed by a single command or button click. Errors detected at any step will prevent execution of following steps. LECTURE 1 40

From a High-level Program to an Executable Code Picture 2

Programmer

Code

Code

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Executable Code

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Program Development (cont.) Loader: – Loads executable code/program into main memory

Execution: – The last step is to execute the program

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Integrated Development Environments (IDEs) • An integrated development environment, or IDE, combine all the tools needed to write, compile, and debug a program into a single software application. • Examples are Microsoft Visual C++, Borland C++ Builder, CodeWarrior, etc.

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Integrated Development Environments (IDEs)

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ANSI/ISO Standard C++ • C++ evolved from C • C++ designed by Bjarne Stroustrup at Bell Laboratories in early 1980s • C++ programs were not always portable from one compiler to another • In mid-1998, ANSI/ISO C++ language standards were approved LECTURE 1

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