Intro to Programming: Basic Definitions

Transcription

1 Intro to Programming: Basic Definitions Programming: The planning, scheduling, or performing of a task or event Computer program: A sequence of instructions for a computer to execute Computer: An electronic, programmable device that can store, retrieve, and process data Data: Information to be processed by a computer Must be in form computer can understand Computer system consists of 2 general components: 1. Hardware 2. Software 1

2 Intro to Programming: Hardware Represents physical components 2 general types 1. Computer proper 3 major subsystems: (a) Main memory (see below) (b) Bus - Primary communication path among components Bus width refers to number of bits that can be transferred across it at one time (c) Central Processing Unit (CPU) Based on von Neumann architecture: Stored program concept Sequential execution 2. Peripherals Add-ons E.g., printer, DVD drive, hard disk 2

3 Intro to Programming: Main Memory Stores everything used by the computer: programs, data,... Stored electronically Uses bi-stable (two-state) device - transistors Transistor is an electronic switch Can be turned on and off As a result, each transistor can represent 2 values Values represented as 1 and 0 Transistor represents a bit(binary digit) of data Memory consists of a linear sequence of storage locations (cells, words,...) Byte considered basic unit of storage 1 byte = 8 consecutive bits Each byte has a unique address, numbered from 0 to total amount of memory - 1 Greek prefixes used for size: kilo = 1,000 mega = 1,000,000 giga = 1,000,000,000 Often, bytes grouped together into words 3

4 Intro to Programming: Main Memory (2) All data stored in memory as sequence of bits This is binary (base 2) representation 2 types of memory: 1. RAM (Random Access Memory) When power turned off, all switches open Memory becomes Volatile 2. ROM (Read Only Memory) Data permanently stored Hardwired Stores parts of operating system needed to start computer 4

5 Collection of programs Types of programs: Intro to Programming: Software Operating system: (Set of) program(s) that control the operation of the computer (e.g., Windows, Mac OS X, Linux) Utilities: Programs that facilitate work (e.g., compilers (see below), calculators) Applications: Programs written to do a specific task (e.g., Word, Excel, Oracle) Software written using a programming language Types of languages: 1. Machine language Each instruction is in pure binary format For example: Problems: Instructions not easy to remember Easy to make mistakes Hard to find mistakes Programmer must manage memory 5

6 2. Assembly language Intro to Programming: Software (2) Uses mnemonic instructions 1:1 correspondence between assembly language and machine language For example: LDA 96 ADC 6 STA 97 CPU cannot directly execute program cause not binary Assembler: program that converts assembly language into machine language Comparison to machine language: Easier to understand than machine code Make fewer mistakes Easier to correct mistakes Requires extra step (assembly) Every time change code, must re-assemble 3. High-level languages 6

7 Intro to Programming: High-level Language Uses English-like instructions Uses symbolic references (variables) to memory For example: x = y + 6 Example languages: BASIC, FORTRAN, COBOL, C, C++, Lisp These are independent of any CPU Must be converted to machine language 2 approaches: 1. Interpreter Reads one HL instruction at a time Translates that instruction to machine code Executes the machine code Repeats until every HL instruction executed 2. Compiler Entire HL program converted into a machine language program Machine program executed Source code refers to program written in a high-level language Object code refers to result of compilation (or interpretation) 7

8 Intro to Programming: High-level Language (2) Comparison of interpreter v compiler Interpreters: Programs execute slowly (must wait for each instruction to be translated) Catch errors exactly where they occur Compilers: Programs execute fast (cause is machine code) Generated errors may occur far from the actual problem Programs must be recompiled after every change There must be a compiler/interpreter for every family of chips Comparison of high-level v low-level languages Low-level: Most efficient code Can take advantage of chip s special features High-level Faster to write ( 10X faster) Self-documenting Allows programmer to ignore low-level details Portable 8

9 Intro to Programming: Language Paradigms There a small number of models on which programming laanguages are based 1. Imperative Based on the concept of an algorithm Programs consist of a state and a statement sequence that changes the state State can be thought of as a set of values (variables) Based on the von Neumann architecture Examples: C, FORTRAN, BASIC 2. Functional Based on the concept of mathematical functions Programs consist of a set of functions Tends not to have state Computation achieved by functional composition (e.g. x + (y (z/15))) Examples: Lisp 3. Declarative Based on logic Programs consist of a set of facts and rules Program states what is to be computed, not how to do so Examples: Prolog 4. Object-oriented Based on objects Programs consist of a set of objects and means for them to communicate Examples: C++, Java, Visual Basic 9

10 Intro to Programming: Object Oriented Programming - Classes Group of objects with similar properties Class describes a set of objects Class consists of members: 1. Attributes Represent characteristics common to all objects states Implemented as instance variables 2. Methods Represent operations that can be performed on/by objects Implemented as subroutines (procedures, functions) Example: car Instance variables: make model owner year engine... Methods: start() fuelup() steer() accelerate()... 10

11 Intro to Programming: Object Oriented Programming - Objects Represent specific examples (instances) of a class Characterized by: 1. State - Set of attributes (instance variables) and the values that describe the object 2. Behaviors - Set of actions (methods) the object can perform The state and behaviors of an object are inherited from its parent class Example: mycar State: make = Saturn model = SLI owner = J Doe Year = Behaviors: start() fuelup() steer() accelerate()... When referring to state and behavior of an object, use following notation mycar.owner mycar.start()... 11

12 Intro to Programming: Language Components Every language consists of a small set of conceptual components 1. An alphabet The set of symbols from which the language is constructed 2. Reserved words The set of words with special meaning in the language 3. Syntax The rules governing valid sentences in the language Rules called a grammar 4. Semantics The meaning behind the constructs of the language Learning a language is learning these components 12