Principles of Computer What is a computer? Science I What is - PDF document

Lecture Outline Principles of Computer  What is a computer? Science I  What is computer science?  Course mechanics Prof. Nadeem Abdul Hamid  Hardware & programming overview CSC 120 – Fall 2005 Lecture Unit 1 - Introduction  Compiling & running Java programs  Binary numbers 1 CSC120 — Berry College — Fall 2005 2 Portions based on Python Programming: An Introduction to Computer Science by John Zelle What is a ‘computer’? Modern Computers  What have you used a ‘computer’ for?  “A machine (?) that stores and manipulates information under the control of a  Writing a paper… balancing checkbook… playing changeable program.” games…  Two key elements to definition:  Computers also used to…  Device for manipulating information  Predict the weather… design airplanes… make  Calculators, gas pumps also manipulate info… but movies… run businesses… perform financial these are built to only perform single, specific tasks transactions… control factories…  Operate under control of a changeable program  How can one device perform so many tasks?  Can provide step-by-step instructions to a computer telling it what to do  What exactly is a ‘computer’?  By changing the computer program , can get the computer to perform different tasks 3 4 A Universal Machine Programming  Every computer is a machine for executing  Software (programs) control hardware (the (carrying out) programs physical machine)  Many different types of computers  Building software = programming  Macintoshes, PCs…  Challenging  Thousands of other kinds of computers, real and  See the big picture while paying attention to small details, but… theoretical  Anyone can learn to program  Remarkable discovery of computer science:  Become a more intelligent user of computers  All different types of computers have same power  Fun  With suitable programming, each computer can  Career basically do all the things any other can 5 6 1

Computer Science (CS) Role of Algorithms in CS  Is NOT “the study of computers”  Dijkstra: computers are to CS as telescopes are to astronomy  Fundamental question of CS: What can be computed?  Computers can carry out any process we describe  So, what processes can be described in order to solve problems?  Algorithm : Step-by-step process to solve a problem 7 8 Algorithms in CS Subareas of CS  Architecture hardware-software interface  Step-by-step process that solves a problem  Artificial Intelligence thinking machines  More precise than a recipe  Eventually has to stop with an answer  Computational Geometry theory of animation, 3-D models  General description of a process rather than specific to a  Graphics from Windows to Hollywood computer or programming language  Operating Systems run the machine  Scientific Computing weather, hearts  Areas of CS discipline span  Theory (mathematics)  Software Engineering peopleware  Experimentation (science)  Theoretical CS analyze algorithms, models  Design (engineering) Many other subdisciplines… networking, numerical and symbolic  computation, bioinformatics, databases and information retrieval, web and multimedia design, security, human-computer interaction… 9 10 Assignments Course Mechanics  Weekly lab/homeworks  Syllabus, lectures notes, assignments, etc. on web page  Due on Wednesdays http://fsweb.berry.edu/academic/mans/nhamid/classes/cs120/05fall   Class meetings  Programming Projects Lectures: Mon/Wed/Fri, 10-10:50AM, SCI 107  Labs: Thurs, 3–5PM, SCI 228   DON’T WAIT UNTIL DAY/NIGHT BEFORE TO  Contact START WORKING ON ASSIGNMENTS Office: SCI 354B — Phone: 368-5632   No late work accepted, without formal excuse/prior Email: nadeem@acm.org  arrangement  Office Hours  You will NOT be able to complete the programming Mon — 11AM–12:30PM  assignments in one night Tue — 11AM–12:30PM  Wed — 11AM–12:30PM and 2–4PM   Send email if you have a problem (attached Thu — 10AM–12:30PM and 2-3PM  relevant files and say where you’re stuck) (or by appointment…)  11 12 2

Programming Assignments Materials and Resources  Completed programs must ‘work’!!!  Textbook:  Java Concepts, 4th Edition , Cay Horstmann  Compile and run (will learn what that means later)  Online course website: Check regularly  If you leave programming assignments to  Software (in computer lab SCI 228) the last minute, you will run a major risk of  Java 5.0 (JDK): http://java.sun.com/j2se/1.5.0/download.jsp having incomplete work  Compiler; runtime system  DrJava: http://www.drjava.org  Editor; development environment 13 14 Grading and Evaluation Hardware Basics  Class participation and attendance (10%)  Lab participation and attendance (10%)  Assignments/Projects (40%)  Exams (40%) Tentative dates:  First exam: Friday, September 23, 2005  Second exam: Friday, October 28, 2005  Final exam: ???  Policies (see syllabus)  Attendance  Academic integrity  Late work  Disabilities 15 16 Central Processing Unit (CPU) Memory  Heart and brain of the machine  Stores programs and data  Chip composed of transistors, wiring  CPU can only directly access info. in main  Two primary components memory or primary storage (RAM- random  Arithmetic/Logic Unit (ALU) performs arithmetic access memory) and logical operations  Relatively expensive  Control Unit controls the order in which  Volatile (loses data when no power) instructions in the program are executed  Secondary storage- more permanent  Hard disk  Floppy, CD, DVD, tape, … Pentium (left) and PowerPC G3 chips 17 18 3

RAM - Main Memory Peripheral Devices  Input Devices  Ordered sequence of storage cells  keyboard  Each holds one piece (a ‘word’) of data  mouse  ‘Data’ is a sequence of bits (on/off - 0/1)  Output Devices  8 bits = 1 byte  printer  video display  LCD screen  Each memory cell has a unique address  Auxiliary Storage (integer number)  disk drive  CD-ROM drive  DVD-ROM drive 19 20 Fetch-Execute Cycle Machine Code  How the CPU operates  Instructions/operations that CPU ‘understands’  Fetch the next instruction  Different vendors (Intel, Sun, IBM) use  Decode the instruction into control signals different sets of machine instructions  Get data if needed (from memory)  Execute the instruction  Extremely primitive Input Main Output CPU  Encoded as (binary) numbers devices Memory devices ALU, registers Bus 21 22 Programming Languages High-level Languages  Could we use English to give instructions to a  Designed to be used and understood by humans computer?  C, C++, Java, Perl, Scheme, BASIC, …  “I saw the man in the park with the telescope.”  All have well-defined, unambiguous syntax and  Who had the telescope? Who was in the park? semantics  ‘Natural languages’ are full of ambiguity and imprecision  Made up for by lots of redundancy and shared human knowledge  Problem:  Computer scientists design precise notations for  Humans write code (programs) in high-level languages expressing instructions/statements: programming  Computers only ‘understand’ machine language (0’s, 1’s) languages  Programming languages have structures with  Compiler : Program that translates programs from high-level language to machine code  Precise form ( syntax )  Precise meaning ( semantics ) 23 24 4

Caveats Java Programming Language  Programs we write in this course will not be fancy  Benefits  Today’s sophisticated programs/games built by teams of highly skilled programmers, artists, other professionals  Simple (compared to C++)  Java language  Safe (security features prevent many ‘bad’ things)  Was designed for professionals, not students  Platform-independent (‘write once, run anywhere’)  Evolving - features change with different versions (we’ll be  Rich library (packages) using 5.0)  Cannot learn all Java in one semester  Lots of code already written for you to do lots of stuff  In fact, no one can hope to learn entire Java library in a  Designed for Internet (applets) lifetime…  Goal of this course: Learn how to think about problem solving and expressing precise solutions using a programming language 25 26 Writing a Program Software Life Cycle Specify the problem  remove ambiguities  identify constraints  Problem-solving and design  Develop algorithms, design   Implementation classes, design software architecture Problem-solving phase  Maintenance Implement program  Algorithm revisit design  test, code, debug  Problem revisit design  Documentation, testing,  maintenance of program Code From ideas to electrons   No shortcuts! Implementation phase 27 28 Writing and Compiling a Java Algorithms and Programs Program Using DrJava IDE = Integrated Development Environment  Algorithm  instructions for solving a problem in a finite amount of time using a finite amount of data  expressed in a precise, but general, way (using English?), independent of type of computer  Program  an algorithm written for a computer using a particular computer/programming language 29 30 5