Download SIT102 Introduction to Programming

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
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
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
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
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
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
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
Fetch-Decode-Execute Cycle
Instruction
Cycle
Control Unit
1
Fetch
Decode
2
CPU
RAM
Execution
Cycle
Store
4
3
Execute
Arithmetic/Logic Unit
SIT102 Introduction to Programming
Lecture 1, Page 8
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
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
Computer Software
Types of software
Software
SIT102 Introduction to Programming
Lecture 1, Page 11
Software
Application Programs
Word processors
Game programs
Spreadsheets
Data base systems
Graphics programs
Web browsers
SIT102 Introduction to Programming
Systems Programs
Operating system.
Networking system.
Programming
language software.
Web site server.
Data backup.
Lecture 1, Page 12
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
ASCII Table
14
ASCII representation
• From 00000000 to 11111111; 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 : 00110001
Integer 1 : 00000001
SIT102 Introduction to Programming
Lecture 1, Page 15
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
Three General Types of Programming Languages:
•
1940s – Machine Languages
•
1950s – Symbolic/Assembly languages
•
1960s – High-Level Languages
•
Note:
Machine and assembly languages are low-level languages because they both use
instructions that are directly tied to one type of computer
– A natural language of a computer, machine dependent
– the only language that can be understood and processed directly by computer
– use of a series of mnemonics to represent commonly used instructions
– E.g. COBOL, FORTRAN, C, Java
SIT102 Introduction to Programming
Lecture 1, Page 17
History of languages
SIT102 Introduction to Programming
Lecture 1, Page 18
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:
11000000000000000001000000000010
11110000000000000010000000000011
SIT102 Introduction to Programming
Lecture 1, Page 19
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
Assembly Language (continued)
SIT102 Introduction to Programming
Lecture 1, Page 21
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
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
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
Writing, Editing, Compiling and Linking
Programs
Type in a program
The object
code
Editor
Linker
Language syntax
The source
program
An executable
program
Compiler
SIT102 Introduction to Programming
Lecture 1, Page 25
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
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
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