SIT102 Introduction to Programming

Transcription

1 SIT102 Introduction to Programming After working through this session you should: Understand the relationships between operating systems, their user interfaces, and programs; Understand the difference between low-level and high-level code; and Understand that code must be converted to machine code, by a compiler or interpreter, in order to run that code on a computer. SIT102 Introduction to Programming Lecture 1, Page 1

2 Computer and Computer Science: Definition A computer is an electronic device, which can input, process, and output data. input processing output A computer is a machine that stores data, interact with devices, and execute programs (provides computing capabilities to its users). A computer Science is the discipline that seeks to build a scientific foundation for such topics as computer design, computer programming, information processing, and algorithmic solutions of problems. SIT102 Introduction to Programming Lecture 1, Page 2

3 Major Components of a Computer System A computer system consists of two main parts: hardware and software. Hardware is the electronic and mechanical parts of a computer system. Software is the data and the computer programs of a computer system. SIT102 Introduction to Programming Lecture 1, Page 3 1-3

4 Computer Hardware Computer hardware is divided into three major Components: 1. The Central Processing Unit (CPU) 2. Computer memory 3. Input/Output (I/O) devices Basic hardware components SIT102 Introduction to Programming Lecture 1, Page 4

5 CPU The CPU is the "brain" of the computer system. It does the fundamental computing within the system It directly or indirectly controls all the other components The CPU has a limited storage capacity. It relies on memory to hold data and programs and to save results. The CPU consists of: 1. The Arithmetic and Logic Unit (ALU). 2. The Control Unit (CU). 3. Registers. The CPU components are connected by a group of electrical wires called the CPU bus. SIT102 Introduction to Programming Lecture 1, Page 5

6 CPU The CPU is connected to memory and I/O devices by the System bus The System bus consists of: Address-, Control- and Data-buses. PC: Program Counter Register MAR: Memory Address Register MDR: Memory Data Register SIT102 Introduction to Programming Lecture 1, Page 6

7 Fetch Decode Execute Cycle The CPU continuously transfers data to and from the primary memory Data transfer is done in units called instructions or words When a computer is switched on, the CPU continuously goes through a process called fetch-decode-execute cycle: The Control Unit fetches the current instruction from memory, decodes it and instructs the ALU (Arithmetic Logic Unit) to execute the instruction. The execution of an instruction may generate further data fetches from memory The result of executing an instruction is stored in either a register or RAM SIT102 Introduction to Programming Lecture 1, Page 7

8 Fetch-Decode-Execute Cycle 1 Fetch Control Unit 2 Instruction Cycle Decode CPU RAM Store 4 3 Execution Cycle Execute Arithmetic/Logic Unit SIT102 Introduction to Programming Lecture 1, Page 8

9 Software Software a group of programs Program a specific set of instructions to the computer to perform a task Programmer a person who writes a program SIT102 Introduction to Programming Lecture 1, Page 9

10 Software Software is the programs and data that a computer uses. Programs are lists of instructions for the processor Data can be any information that a program needs: character data, numerical data, image data, audio data, etc. Both programs and data are saved in computer memory in the same way. Computer software is divided into two main categories: 1. Systems software 2. Applications software System software manages computer resources and makes computers easy to use. An applications software enables a computer to be used to do a particular task. SIT102 Introduction to Programming Lecture 1, Page 10

11 Computer Software Software Types of software SIT102 Introduction to Programming Lecture 1, Page 11

12 Software Application Programs Systems Programs Word processors Game programs Spreadsheets Data base systems Graphics programs Web browsers Operating system. Networking system. Programming language software. Web site server. Data backup. SIT102 Introduction to Programming Lecture 1, Page 12

13 Data representation Represented by a combination of eight binary digits (1s and 0s) ASCII American Standard Code for Information Interchange SIT102 Introduction to Programming Lecture 1, Page 13

14 ASCII Table 14

15 ASCII representation From to ; each assigned to a unique character. An integer is stored in memory in its binary equivalence read as character using its ASCII character The number 1 can be stored in many ways depending on how the data is interpreted by a given program. Character 1 : Integer 1 : SIT102 Introduction to Programming Lecture 1, Page 15

16 Programming Languages Computer program: data and instructions used to operate a computer and produce a specific result Programming: writing instructions in a language that the computer can respond to and that other programmers can understand Programming language: set of instructions that can be used to construct a program Source programs/source code: Programs written in a computer language SIT102 Introduction to Programming Lecture 1, Page 16

17 Three General Types of Programming Languages: 1940s Machine Languages A natural language of a computer, machine dependent the only language that can be understood and processed directly by computer 1950s Symbolic/Assembly languages use of a series of mnemonics to represent commonly used instructions 1960s High-Level Languages E.g. COBOL, FORTRAN, C, Java Note: Machine and assembly languages are low-level languages because they both use instructions that are directly tied to one type of computer SIT102 Introduction to Programming Lecture 1, Page 17

18 History of languages SIT102 Introduction to Programming Lecture 1, Page 18

19 Machine Language Executable program: program that can operate a computer Executable programs are written with binary numbers, which is a computer s internal language (machine language) An example of a simple machine language program containing two instructions is: SIT102 Introduction to Programming Lecture 1, Page 19

20 Assembly Language Assembly language: uses the substitution of wordlike symbols for the opcodes, and decimal numbers and labels for memory addresses EG: z = x + y In assembly Mov ax, x Add ax, y Mov z, ax In C# z = x + y; SIT102 Introduction to Programming Lecture 1, Page 20

21 Assembly Language (continued) SIT102 Introduction to Programming Lecture 1, Page 21

22 Earlier high-level programming languages COBOL (Common Business Oriented Language) used primarily for business processing FORTRAN (Formula Translation) primarily perform mathematical calculations SIT102 Introduction to Programming Lecture 1, Page 22

23 Later High-Level Programming Languages PL/I, BASIC, Pascal, Prolog, C, Ada C++, Visual Basic, C# HTML, Java SIT102 Introduction to Programming Lecture 1, Page 23

24 Writing, Editing, Compiling and Linking Programs Step1 Write and edit programs Step2 Compile programs Translate source file into machine language The output produced by the compiler is called an object program (machine language version of the source code) Step3 Linking Programs - combines additional machine language code with the object program to create a final executable program SIT102 Introduction to Programming Lecture 1, Page 24

25 Writing, Editing, Compiling and Linking Programs Type in a program The object code Editor Language syntax Linker The source program An executable program Compiler SIT102 Introduction to Programming Lecture 1, Page 25

26 Procedural and Object-Oriented Languages Structured language: high-level procedural language (e.g., C) that enforces structured procedures Object-oriented languages: languages with object orientation such as C++, Java, Visual Basic, and C# SIT102 Introduction to Programming Lecture 1, Page 26

27 The Making of A Quality Program 1. Readability understandable, with comments and documentations, using conventions like name of variables and indentations 2. Modularity problems divided into sub-problems and assembled in a logical order 3. Efficiency runs faster and smaller size of program SIT102 Introduction to Programming Lecture 1, Page 27

28 The Making of A Quality Program (cont.) 4. Robustness Be able to handle all situations in a graceful manner Not to crash in unexpected situations or go to infinite loops 5. Usability correct, meets the end-user requirement SIT102 Introduction to Programming Lecture 1, Page 28