Introduction to Computers and Programming Languages (Part 1)

Transcription

1 Introduction to Computers and Programming Languages (Part 1) Computer Fundamentals Computer system is divided into hardware and software. Hardware refers to physical components of computer which are: o Main Memory o Central Processing Unit (CPU) o Input Device o Output Device o Secondary Memory Device Figure example of processors (CPU) The Intel Atom processor chip contains the full circuitry of a central processing unit in an integrated circuit whose small size and low power requirements make it suitable for use in mobile internet devices. (Intel Corporation Pressroom Photo Archives) Figure Types of Computers (a) Notebook Computer (HP Pavilion dv5, Courtesy of Hewlett-Packard). (b) Palmtop Computer (iphone 3G, Courtesy of Apple, Inc.) (c) Desktop Computer (imac, Courtesy of Apple, Inc.) 1

2 Figure 1.3 Components of a Computer PGT106 C PROGRAMMING Input Device CPU Control Unit Arithmetic and Logic Unit Register Output Device Main Memory Secondary Memory Central Processing Unit (CPU) o CPU is the computer s administrator and is responsible for supervising the operation of the other sections o Consists of two functional units; control unit - supervises all activities of the computer system arithmetic-logic unit (ALU) - performs basic arithmetic operations and comparison operations 2

3 Main Memory o keeps information from the input unit. o Used only during processing of data. o also keeps processed information until it can be placed on output devices o all programs must be loaded into main memory before they can be executed and all data must be brought into main memory before it can be manipulated. o However, the data/information is temporary. It will be discarded after a program ends, or when the computer is turned off. o Main memory can be further classified into two types: Random Access Memory (RAM) - information in RAM will be lost when the computer is turned-off. Read Only Memory (ROM) - It has been set during manufacturing process. ROM usually contains instructions and information considered to be fundamental to the computer. o Figure 1.4 Visual representation of 1000 Memory Cells in Main Memory Secondary Memory/ Secondary storage o Stores information permanently (as compared to temporary information retain of main memory) o The stored information can be retrieved later. o Examples of information/data that is stored : program file, data file, image file, etc o Examples of secondary storage devices: hard disk, diskette, CD, USB drives, etc (refer to figure 1.3) 3

4 Input/Output Devices o Input devices feed data and programs into computers e.g. keyboard, mouse, touch screen, scanners o Output devices display results produced by computer e.g. monitor, printer, speaker Software o As a complement to hardware, computer system needs software to work/function. o Softwares are classified into : System software Application software Programming Languages o System software : manages the computer and its peripheral devices (hardware) E.g. Operating system (OS) Text editor Pre-processor Language translator Linker Loader o Application software : performs specific tasks E.g. word processor, desktop publishing software, spreadsheets, database, graphics, communication, programs perform specific tasks such as accounting, scientific, engineering, education, etc Programming Fundamentals Programming Languages o Programming language is divided into three categories: Machine Language Assembly Language High-Level Language o Machine Language Language understood by the computer Bunch of 0 s and 1 s (binary code) Program written in machine language can be executed without being translated Nevertheless, hard to learn because it is written in 0 s and 1 s Program is too long to solve simple problem Machine-dependant and not portable E.g

5 Figure 1.6 Relationship Between a Byte and a Bit o Assembly Language Strings of 0 s and 1 s are replaced into instructions which resemble English language to represent computer operation element Easier to understand and write E.g. LOAD MULT STOR rate hour wages Nevertheless, needs a language translator called Assembler to change Assembly Language to Machine Code for execution purpose still too long and not portable o High-Level Language Improves weaknesses in Machine Language and Assembly Language Easier understood because it is closer to natural language (especially English) Portable (Can be executed on more than one platforms/ environments) Written in one instruction to carry out several instructions in machine level E.g. discount_price = price discount; needs a compiler : a system software that translates source program to object program - translates the codes into machine language Examples: - C, C++, Java, Visual Basic, Pascal. Algorithms o Refers to the solution to any computing problem which involves executing series of actions in a specific order (step-by-step instructions) o Represented in writing, and can be replicated (used again and again) 5

6 o Two most common ways of representing an algorithm: Pseudo code Flow chart o Pseudo code : artificial and informal language that helps programmers develop algorithms E.g. : Start Get student s grade. if student s grade is greater than or equal to 50 Print Pass else Print Fail End o Flowchart: visual-form of an algorithm E.g. start Read grade grade >= 50 True Print Pass False Print Fail end o Basic symbols in a flowchart Terminator (start/ end) Direction flow Process connector Input/ output (data) Decision 6

7 Basics of a Typical C Program Development Environment 7

8 Figure 1.7 Entering, Translating, and Running a High-Level Language Program Figure 1.8 Flow of Information During Program Execution 8

9 Simple C Program: Program to add two numbers o For starters, just remember that a program MUST include the parts marked as *. * #include <stdio.h> int main() { int da, db, dsum; printf ( Input first integer \n ); scanf ( %d, &da); printf ( Input second integer \n ); scanf ( %d, &db); * } dsum = da + db; printf ( Sum is %d\n, dsum); return 0; 9