COMP 14 Intro to Intro to Programming May 23 2000 Nick Vallidis What we ll talk about today Brief overview of computers Hardware and Software What is programming Java Algorithms Computers Basically information processors Take info do something to it spit it out again Digital Store the information as numbers digits Use the binary number system Computers 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 printer Our view of the hardware Monitor Keyboard Central Processing Unit Secondary Memory Hard Disk Main Memory Floppy Disk CPU Central Processing Unit Continuously does fetch decode execute Retrieve an instruction from main memory fetch execute Carry out the instruction decode Determine what the instruction is Memory An address is the name of a specific location in memory Main Memory run programs from here fast volatile Secondary Memory slow permanent This 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 write Computer 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 BASIC Compilers 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 directly Java is compiled and interpreted Java source code Java compiler Java bytecode Java interpreter Bytecode compiler Machine code So 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 implementation Implementation Not any more important than other steps but probably the one you know the least about We are using Java Simple Java Program public class Simple public static void main String args System out println Hello Simple Java Program public class Simple All programs have to be part of a class public static void main String args System out println Hello Simple Java Program public class Simple Tells the computer where to start running the program public static void main String args System out println Hello Simple Java Program public class Simple public static void main String args System out println Hello Braces indicate where different sections of the program begin and end Simple Java Program public class Simple public static void main String args System out println Hello This tells the computer to print out Hello without quotes Simple Java Program public 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 Program public 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 purpose Java Reserved Words abstract boolean break byte byvalue case cast catch char class const continue default do double else extends false final finally float for future generic goto if implements import inner instanceof int interface long native new null operator outer package private protected public rest return short static super switch synchronized this throw throws transient true try var void volatile while Simple Java Program public 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 sensitive Simple Java Program public class Simple Red identifiers were chosen by the author of this program public static void main String args System out println Hello Blue 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 letter Comments 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 user public 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 instructions Homework 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 sandwich