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COMP 14: Intro. to Intro. to ProgrammingWhat we’ll talk about today...ComputersComputers are made of 2 thingsHardwareOur view of the hardwareCPUMemoryThis class is about SoftwareComputer LanguagesCompilers and InterpretersJava is compiled and interpretedSo what is programming?ImplementationSimple Java ProgramSlide 16Slide 17Slide 18Slide 19Slide 20Slide 21Java Reserved WordsSlide 23Java IdentifiersSlide 25Identifier guidelinesCommentsSlide 28AlgorithmsHomeworkCOMP 14: Intro. to Intro. to ProgrammingMay 23, 2000Nick VallidisWhat we’ll talk about today...Brief overview of computersHardware and SoftwareWhat is programming?JavaAlgorithmsComputersBasically “information processors”–Take info, do something to it, spit it out againDigital–Store the information as numbers (“digits”)Use the binary number systemComputers are made of 2 thingsHardware–The part you can see and touch–CPU, monitor, mouse, keyboardSoftware–Information to tell the computer HOW to process information–OS, compiler, word processor, games, etc.HardwareCPU: Pentium (II/III), Alpha, AthlonMemory: RAM, floppy disk, hard drive, CDInput Devices: keyboard, mouse, data tabletOutput Devices: monitor, printerOur view of the hardwareMonitorKeyboardMainMemoryCentralProcessingUnitFloppy DiskHard DiskSecondary MemoryCPU“Central Processing Unit”Continuously does fetch-decode-executefetchRetrieve an instruction from main memoryRetrieve an instruction from main memorydecodeDetermine what theDetermine what theinstruction isinstruction isexecuteCarry out theCarry out theinstructioninstructionMemoryAn address is the name of a specific location in memoryMain Memory–run programs from here–fast, volatileSecondary Memory–slow–permanentThis class is about SoftwareOperating System (OS)–Understands the hardware–Simplifies your interaction with the hardware–Controls starting/stopping applicationsApplications–any software that isn’t the OS–what you will learn to writeComputer LanguagesMachine Language–the form the CPU understands–strings of 1’s and 0’sAssembly Language–people-friendly version of machine languageHigh-level languages–Java, C++, FORTRAN, COBOL, BASICCompilers and InterpretersBoth are ways to turn high-level languages into something the computer can executeCompilers turn a source code file into an executableInterpreters let you type the program into it and run it directlyJava is compiled and interpretedJava sourcecodeMachinecodeJavabytecodeJavainterpreterBytecodecompilerJavacompilerSo what is programming?Programming IS problem solvingTakes multiple steps:–understand what the problem is–find a solution (algorithm) for the problem–determine if the solution is correct–implement the solution–test the solution implementationImplementationNot any more important than other steps, but probably the one you know the least aboutWe are using JavaSimple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}Simple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}All programs have to be part of a classSimple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}Tells the computer where to start running the programSimple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}Braces indicate where different sections of the program begin and endSimple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}This tells the computer to print out “Hello!” (without quotes)Simple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}This indicates the end of a statement (one “step” in the program)Simple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}These are reserved words in Java. This means that Java uses them for a special purposeJava Reserved WordsabstractbooleanbreakbytebyvaluecasecastcatchcharclassconstcontinuedefaultdodoubleelseextendsfalsefinalfinallyfloatforfuturegenericgotoifimplementsimportinnerinstanceofintinterfacelongnativenewnulloperatorouterpackageprivateprotectedpublicrestreturnshortstaticsuperswitchsynchronizedthisthrowthrowstransienttruetryvarvoidvolatilewhileSimple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}These are identifiers. These are words chosen by a programmer as names for things.Java IdentifiersCan include letters, digits, $, and _Must not start with a digitThey are case sensitiveSimple Java Programpublic class Simple{public static void main(String[] args){System.out.println(“Hello!”);}}Red identifiers were chosen by the author of this programBlue identifiers were chosen by another programmer.Identifier guidelinesYou want to choose descriptive identifiers–things like a, b, dm, tu are bad–things like lastValue, $cost are goodIf multiple words, start each new word with a capital letterCommentsYou can insert comments in the code that are completely ignored by the compilertwo styles:–/* everything in here is a comment */–// everything to the end of line is a commentI was very bad and didn’t comment the program I showed before. Let’s fix that...Simple Java Program/* a very simple Java program */public class Simple{// prints a message to the userpublic static void main(String[] args){System.out.println(“Hello!”);}}AlgorithmsA step-by-step description of a solution to a problemIn some sense the computer is stupid and needs very explicit instructionsHomeworkRead Ch. 1 (there are more specific instructions on the web page, but it’s ok if you just read the whole thing)Write an algorithm for making a peanut butter and jelly


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UNC-Chapel Hill COMP 14 - COMP 14- Introduction

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