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Overview of the Computer

Overview of the Computer. Definition : a programmable device that can store, retrieve, and process data. Hardware = physical components of a computer Software = computer programs (the set of all programs available on a computer). application software and system software.

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Overview of the Computer

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  1. Overview of the Computer • Definition: a programmable device that can store, retrieve, and process data. • Hardware = physical components of a computer • Software = computer programs (the set of all programs available on a computer). • application software and system software. cosc236/intro

  2. Computer components: cosc236/intro

  3. Programming Language • Definition: languages with strict grammar rules, symbols, and special words used to construct a computer program cosc236/intro

  4. Machine language • the language that can be directly used and understood by the computer • operations are very low-level, specific to the architecture (not portable) • made up of binary-coded instructions (strings of 0s and 1s) • exa: 110011 - add instruction cosc236/intro

  5. Assembly Language • A low-level programming language in which a mnemonic is used to represent each of the machine language instructions for a particular computer • Requires assembler cosc236/intro

  6. COMP$PAY PROC PUBLIC ; ; COMP$PAY - procedure to compute gross pay ; (PAY = HOURS * RATE) MOV AX,HOURS ; multiplicand MUL RATE+2 ; X second word of multiplier MOV PAY+2,AX ; store the product in PAY ; MOV AX,HOURS ; multiplicand MUL RATE ; times first word of multiplier ADD PAY+2,AX ; add the product to PAY ADD PAY,DX ; add the carry, if any RET ; end procedure cosc236/intro

  7. High-level languages • Basic, C++, Pascal, Java, Ada, Modula-2, Cobol, Fortran… • Similar to natural language (easier to use and debug) • standardized description of the language exists cosc236/intro

  8. High-level languages cont’d • Not understood directly by a computer, must be converted to machine language: • Compilers: whole program is translated into another language (machine language or bytecode) and then executed • Interpreters: program is translated and executed one line at a time • portable (machine-independent) • Program is written for any platform • compiler translates to each platform cosc236/intro

  9. C++ compiled to machine language • Requires translating to many different machine languages • Java compiled to Java bytecodes • One set of bytecodes can execute on many different machines • intermediate level • machine language for theoretical computer: Java Virtual Machine (JVM) cosc236/intro

  10. Java • Class • Unit of code that is the basic building block of Java programs • Java runtime • JRE • Executes compiled Java class files • Most computers have Java runtimes on their computer cosc236/intro

  11. Background • Released by Sun in 1995 • Object-oriented • Rich libraries – pre-written software • Active programmer community • API Specification • Application Programming Interface • Extremely platform-independent cosc236/intro

  12. Java Advantages • Platform independence • Reuse of code • Security • Automatic garbage collection • Stronger typing of objects and variables Columbia University JETT

  13. Java Programming Environment • Type program as Java class =>.java • Compile => .class (bytecode) • Loader – connects bytecode from various classes and loads bytecode into main memory • Interpreter – translate and run cosc236/intro

  14. Sample program public class Hello { public static void main(String[] args) { System.out.println("Hello World!“); } } cosc236/intro

  15. Java programs • class Hello • Class names begin with capital letter • file Hello.java • Class name and file name must match cosc236/intro

  16. class • Unit of code that is the basic building block of java programs public class <name> //class header { <method> <method> … <method> } main method is required public static void main(String[] args) cosc236/intro

  17. methods • particular action or calculation • main method is required • Method header public static void main(String[] args) { statements } cosc236/intro

  18. statements • Command • Statements end with ; cosc236/intro

  19. System.out.println • Line of output sent to console window • System.out.println("Hello World!“); • System.out.println(); • System.out.print(“Hello”); • //does not move to next line of output cosc236/intro

  20. Literal string • Surrounded by quotes • One line • Escape sequences \t tab \n new line \” quotation \\ backslash • System.out.println(" \"Slick\" Willy"); • "Slick" Willy cosc236/intro

  21. Example System.out.println("This\nyields three lines\nof output\n"); This yields three lines of output cosc236/intro

  22. Identifiers • used to name variables, constants, methods, classes, and data types • Rules: • must start with letter or underscore or $ • Composed of letters, digits, $, or underscore (better to start with a letter) • Using Meaningful, Readable Identifiers! • Java is case sensitive • Don't use reserved words cosc236/intro

  23. Legal: firstName conversion lengthOfRoom payRate counter1 x Illegal first name Hello! 5th one+two Identifiers cosc236/intro

  24. Identifiers - Style • Class name • Begin with capital letter • Method • Begin with lowercase • Exa: calcPay,getInfo, sum • Constants: all caps • PI, MAX_HOURS, UNIV_NAME cosc236/intro

  25. Comments • Compiler ignores comments • /* */ everything between pair is ignored • // - everything after the two slashes to the end of line is ignored • header comment: • //Project number • //Student's name Date project is due • //Course number • //Purpose of the program cosc236/intro

  26. When to use comments • Comment variable and constant declarations. • Precede blocks of code with an explanatory comment. • Explain statements that are not obvious. • Precede each class with a brief header comment cosc236/intro

  27. Readability • Class and method headers on lines by themselves • One statement per line • Indent • Use whitespace liberally in the form of blank lines and spaces. • Include at least one blank line between methods cosc236/intro

  28. Syntax • Syntax - formal set of rules governing how valid instructions are written in a programming language cosc236/intro

  29. Program Errors • Syntax error – error in using Java, indicated by compiler • Cannot execute • Exa: File name does not match class name • Logic error (bug) – code doesn't perform the intended task • debugging cosc236/intro

  30. Structured Programming • Control structures • sequence • selection • Loop • Modularity/Top-Down Design • Decomposition – separation into parts • Functions, procedures => methods cosc236/intro

  31. Static method • A block of statements that is given a name • Static • allows non object-oriented invocation • Use no instance variable of any object they are declared in • Method call • Transfers control • Methods can call other methods cosc236/intro

  32. public class Memo { public static void main(String[] args) { printLogo(); //method call System.out.println("Reminder:" ); System.out.println("Company Meeting"); System.out.println("Thursday at 9:00!!!!"); printLogo(); } /* end main */ public static void printLogo() // method header { System.out.println("*************************************"); System.out.println("**********YOUR COMPANY********"); System.out.println("*************************************"); } } cosc236/intro

  33. Design/Plan the solution • Algorithm – a step by step procedure for solving a problem, ordered set of instructions such that: • programs are implementations of algorithms, emphasis on writing algorithms. • the computer is a fast and flexible tool for implementing algorithms. • tools • flowcharts • Pseudocode • subtasks - hierarchy chart • test solution for correctness - trace cosc236/intro

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